A quantitative analysis of the charge-transfer perturbation model for the cycloaddition of diazoalkanes with olefins

‘Ferrohedron Vol. 43, No. I. pp. 159 to 170, 1987 Pnnkd in Great Britain

A

IlUANTlTATlVE

OO4O-a20/87 ss.oo+ .xl 0 1987 Pqamon Journals Ltd.

ANALYSIS

OF

THE

CYCLOAOOlT1ON

Marina Dipartimento

CHARGE-TRANSFER

OF DIAZOALKANES

Durdisso

di Chimica

V.le Taramelli

MODEL

FOR

THE

and Remo Gandolfi*

Organica,

Universite

10, 27100 Pavia,

Simona Puartieri Oipartimento

PERTURBATION WITH OLEFINS.

di Pavia,

ltaly

and August.0 Rastelli*

di Chimica,

Universita

Via Campi 183, 41100 Modena,

di Modena, Italy

(Received in UK 7 November 1986)

-

Abstract

Non-frontier

investigated and methyl beeing

diazoacetate

The

olefins.

charge-transfer

for the cycloaddition main

negligible,

to a wide

result play

both the regiochemistry

is

interactions

of diazomethane, group

that

of mono

these

a decisive

role

have

and disubstituted

interactions, in the

and the rate of these

been

2-diazopropane far

from

rationalization

of

reactions.

INTRODUCTION A recent conclusions aspects,

book'

about

i.e.

the

the practical

for whatever

from

FO,

not

reactions. reaction

introduce

affinities,

or

averages

first

of

kinds

their

of

LCAO

second

estimates, ionization

it is not surprising

been

agree

to

with

FO theory

perturbation

interesting

molecular

orbital

(FO) approximation. such a high

degree

of "versatility"

After all, the regiochemical

appropriate one

relevance

use

replace

potentials steric

to

pick one

DP = dipole,

figures

or

problem

orbital

it.

to

obtained

calculated been

results

options

one

taken

other

is

as

as

produced

the

as

the

frontier

average

or of

and electron also

HO energies.7 may or not in the

take

one could

potentials energies;

factors

could

orbitals

the

DF = dipolarophile);

ionization

that new regiochemical

159

different

Moreover,

have

of

integrals,

out

(coefficients?)

6

number

non-F0

and electrostatic

and so to support

large

interaction

could

either

d-expansion. may

and a very

as to

or

even

interactions,

most

important

be

approximations,

and

the

most

can

and

problem

on

of

the

from one to the other: one could use plain FO coefficients

useful

Consequently, found

firmly

reached

and a bit of LUDp-HODF,

various

secondary

rests

orbital

has

i.e. mixture)

with and without

and

rate,

summarizes

rationalization

result one has to handle.

the

d-orbitals,

calculated

cycloaddition

Extensive

on its frontier

coefficients

assign

(e.g. HOOP-LUDF

coefficients

different

FO

different

or simply

interaction

of

1,3-dipolar

use of FO theory

(or grey,

products

coefficients

could

and

of

which may switch predictions

squared

"true"

of

experimental

a black-or-white

selected

class

2-5 and, mainly,

However

only

this

chemistry

regiochemistry

(PMO) methods

account

on the

weighted Lastly,

be ignored.

last decade

have

In our opinion, their

even if

non-systematic On the other

complete

hand, one cannot

to that

On the side theoretical

i)

the

of reaction

ignore

rates,

concerns

investigation

the

inclusion

iii)

a further

the

justified,

and uncertain

with

the

practice

of

that

the

predictions.

and Co11.3 had shown,

regiochemistry

most impressive

extensively,

a success

match between

and mainly

that

is,

to

experimental

diazomethane

Sustmann and Coll.

-LUDF) fails (HOD2M

the series

correlations

U-shaped

for several

at

The up-to-date

correlate

the

data

cycloadditions,

least,

and their and is due

conclusions

reaction

rate

predominating

in the

are:

of

series

a

sooner

the extant

of

as

ii)

and the

non-systematic

options

suggestion

'the

ignoring

of ordering

r*=0.86); changes

reaction

of

rates

MO to

for OZM(r*=O.90); lo in

relationship

methyl

evaluated

diazoacetate)

EA’s.

have not

a) accept

the

two

frontier

LUDp-HODFbecoming

that

ignored

results

iii)

the trend

iiii)

the dominant

of U curves and iiiii)

for

could

will

reaction

one in the

HO DP-LUDF left-branch

be read as successes necessary

rates;

be obtained,

the

is only a minor drawback.

of MO coefficients,

to account

correlations

contributions,

for

explaining

b) be willing

and that,

of

to believe

on the contrary,

c)

is incidental.

regiochemistry

the

in

role

1,3-dipoles

The poor quality

Certainly

and criticisms

cycloaddition,

charge-transfer

sum of

are plotted.

the missing

survey

consists

a good linear

type II Ila iii);

the

right-branch

correlation

Zi[HOo2M-Ui oF],

alkenes9

ionization potentials have been obtained of log k2 vs. dipolarophile llb,c and shown to be consistent with the above approximation iii):

must be necessarily

The above

that

the exclusive

obtains

approximation

reactants

or later

(log k2 vs.

MO’s of

(e.g.

but one ought to:

regiochemistry,

FO model,

unoccupied

of log k2 for

A few comments are necessary. FO theory,

correlation

leaving

gaps,

non-frontier

IP’s and empirically

interpreted

where electron-rich

the

involving

gaps are based on the experimental

II 1,3-dipoles,

is

to

of olefins,

relationships

type

U curve

through

linear

energy

the energy

linear

interactions

the requested

of the frontier

correlation

yet been achieved

also

Bastide

for

of Huisgen,

approximation

along

the inverse

In

that

diazoalkanes,

of other

in giving

coefficients

that

reasonably

in weak explanations

can account

FO approximation 9

does succeed

iiiii)

are

olefins,

ii)

iiii)

adjustments

of FO theory.

to the extensive

this

term

counterparts

conjugated

some of these

use can only result

change-transfer

comparable

the

BURDSSO et al.

M.

160

for

strongly

and reaction single

recommend further should

rate,

cases)

procedure

investigation:

be dealt

either

with a single,

in the

FO scheme

molecular

distortions,

both rigid or

in

aspects

of

(i.e.

without

the

complete

model. the effects paper we explore 12 on the FO performance; then by Klopman, present

introducing

a systematic

empirical

reduction

of

we analyze

of the

the

orbital

role

energy

according

of non-F0 gaps,

in

to

a

interactions,

the

undistorted

molecules.

METHODS,MOLECULES ANDDATA MO energies rests

and coefficients

on the following

of CNDO/Zcalculations

arguments:

CNOO/ZFO energies

affinities,

but the same is true to expect

this

PM0 calculations

a) literature

is not the real

b) standard

no good reason

for

also

standard

and experience

results

the experimental

for minimal basis except

ab-initio

for the highest

CNDO/Z quality;

show that

cause of disappointing

do not reproduce

result,

are

the

calculations.

occupied

insufficient

with FO theory

ionization

this

potentials

in this

choice quality field;

and electron

Actually,

there

MO (Koopman’s approximation);

is

161

Charge-transferperturbationmodel c) since our work concerns a widely investigated adoption of the very same procedure favours ortho-normality

C+C=l, explicitly

condition

area, where CNDO/Zhas been in common use, the

the comparison with previous required

by Salem’s

calculations;d) is

model’

fulfilled

the

by CNDO

procedure. For treating distorted

molecules a computer program was assembled for obtaining HO’s using a (HAO)13’14 and the CNDO/2parametrization.

basis of hybrid atomic orbitals

The molecules in study comprehend three l,%dipoles, and methyl diazoacetate alkenes,

diaromethane (OZN), 2-diazopropane (OZP),

(OZA), and about twenty dipolarophiles,

bearing strong acceptor

f-N02, -C02Ne1 and strong

ethene,

conjugated groups (-CH=CH2,-Ph), sulphonyl groups both in open and cyclic list

mono and polysubstituted

donor (-pyrrolidinyl)

substituents,

structures.

The conplete

is given in Table 4. Let us call A and 8 the two possible

bearing heteroatoms in polysubstituted

+

R’R*C N L

adducts from cycloaddition,

and let X be the substituent

alkenes.

RmL -‘x 6

A

Only regioisomer A was, as a rule, detected in the reactions of OZN; mixtures were found only 17.21 16 15 16 Ethyl vinyl ether gave A and thiete l,l-dioxide, and styryl sulphones. 19 N-isobutenyl pyrrolidine did not react. DZA cycloaddition led to B with N-isobutenylpyrrolidine 20 and N-(l-cyclopentenyl)pyrrolidine, whereas the regiochemistry with ethyl vinyl ether has not yet for

propene,

been reported.2’

Relative

cycloaddition

10, and ref.

and Ild,

respectively.

llc

Charge-transfer energies. between an occupied orbital

rate constants for DZNand DZA are taken from ref.

Salem’s expression2 for the energy of charge-transfer

where IAC (=I ei- Ejl is the orbital in i(j),

interaction

k

i and a vacant one j are:

-CTA =2(CCC&C + CNC, YCN>2/t AC 1 Bk -CT k=2KcCa Y cc + CNCaTcNj2/i A e t atoms of 1,3-dipole

9 and

for adduct A for adduct 6

energy gap, Cc and CN are the

T-coefficients

of the terminal

C,

and C are the r-coefficients of the olefinic o and fi carbon B atoms in j(i). The interaction integral y cannot be estimated satisfactorily and must be treated as 22 an empirical parameter; it appeared reasonable to assume the same rules as those adopted in CN00/2 for the evaluation of core resonance integrals

( 6x,= @;ySxy,

PC_=-21

eV, pCN=-23 eV),

where S is the overlap integral between the n-A0 (or r-HA0 in distorted molecules) of the XY reacting centers at a distance of 2.5 A. It may be added that all the conclusions to be reached are largely

independent of the actual values adopted for this distance,

values of 2-3 A. Single charge-transfer HOOP-LUDF; LUDP-HOOF

interactions

in the range of the reasonable

can be summedup into various contributions,

frontier

contributions

z.tio -u. contribution of dipole I Dp I.OF 2. .o total contribution of 1) i,DP-“j ,DF E..U. total contribution of IJ ~,OP-“i,DF LkCTk= 2..0. + z..u. total charge-transfer ‘CT= IJ l,DP-“j,DF 11 ],OP-‘i,OF that have chemical meaning in the charge-transfer mdel. For each

HOW as a donor dipole as a donor dipole as an acceptor energy contribution

a regiochemical

hf. BURDIW

162

index D B A can be calculated Geometries OZM,23

A,

1.30

according

choice

1.139

A,

for

a

single

A;

(30°

values,

23

bond angles

condition

these

are HCH

CCC

criterion

C-C02Me

(DZP):

for

Bond

data

for open

in distorted

the molecular

calculations

on distorted,

i.e. "the orbital(s) decreased

most".

rigid choice both

the

of the

true

CNDO/Z)

and

a) the frontier

orbital

the frontier

in Table

the

on distorted

to

Klopman,

required

calculations,

with

have

energy narrowings

orbital

energy

gaps

been

to

6LU,DF) HO,DP'LU,DP- 'HO,DF A

Exp. or Estimateda

- 'LU,DF) HO,DP 6LU,DP- %O,DF

lPDP-EADF -EADp+IPDF

12

9.0024,ADZA

EA: DZM = -1.BOz6,

=

for

1.336

1,

(exp.), 116.5'

imposing

gain

complete

the

of the bond

an

or

standard

direct

valence

increasing

reaction,

to be formed

this procedure their the

could

almost

reaction

rates.

but they

done,

and

supply

exclusive

will

reaction

SO

that

MO

orbital(s)

whose

Extensive not

weight

energy

FO theory

role

in

is

with

a

determining calculations

be reported

distances

are decreased

(eV) for the reaction

00

are modest

here

Q=300

(DZM) and

to stabilization

of diazoalkanes

with ethene.

cY=OO

DZP

Q=OO

15.48

15.02

14.55

15.79

14.49

16.77

16.05

15.29

14.71

17.00

1.29

1.03

0.74

-1.08

2.51

16.57

15.97

15.43

16.75

15.04

20.60

19.05

19.03

18.60

20.14

4.03

3.80

3.60

1.85

5.10

IO.78

10.98

12.31

11.51

9.2019'2'b~3Ethene

DZA = -1.0019*20a,

= 10.51z5

Ethene = -1.7Bz7

ethene

owing

DZA

cY=ZOO

and unselective;

of diazomethane

0.53 a) TP: DZM =

C=C

l16.Z"

experimental by

and

for Me 1.117

values:

(planar),

FO's

caused by distortion

for the

and LUDp-HODF

energy gaps

-( E

A

C-H

in

are:

orbital

-( E

this

are able to single out the stereodirecting

and demonstrate

O!=

CNDO/Z

(planar);

A.

O-He 1.41

optimized

(20'

geometries

A,

1.506

either

optimized

120.8'

14

DZM

STO-3G

119.9O

of

AND DISCUSSION

correlations

1; both HODp-LUDF

Table 1. Frontier

empirically

direction

molecules

were

values,

(exp.),

unknown

C-Me

A,

126O

are experimental

alkenes

in the region

by actual

FO orbitals

the main conclusions

an example reported

that concentrates

the experimental'value;

(DZA):

and

are: HCH 116.1°

According

molecules

known

B and A (ECT B-ECT A).

calculated

HCC

propene,

for ethene

been

given

C-O 1.36

(atom-following).

in the

isolated

If supported

regiochemistry

(STO-3G and detail;

distortion

A,

C=O 1.21

have

molecules.

for adduct

(planar),

(planar);

from

substituted

procedure

were

123.3“

with

assumed

RESULTS

during

122.B0

lengths

for

systems

to the hybridization

FO analysis

angles

molecules

A,

1.44

the values

(DZM):

from STO-3G optimization,

Geometrical

distorted).

Bond

respectively.

of dipolarophiles.

bond angles,

between

C-N, N-N, C-H were fixed at

Other bond lengths were

and from methylacrylate, Geometries

A

1.075

(30° distorted);

molecules.

C-H 1.089

Bond lengths

calculations;

117.9O

allows

distorted

A,

of 1,3-dipoles.

to STO-36

distorted),

as the difference

et al.

as are

of

Charge-transfer

Table

2.

CNDO/Z energies

trans-phenyl

styryl

(DB A) of

their

( E 1 and

sulphone

interactions

perturbation

coefficients

and

corresponding

with

diazomethane

model

163

C,, 1 of

(Co,

unoccupied

charge-transfer

energies

molecular and

regiochemical

Distorted -1

E(eV)

C,

5.52

.44

-.55

-30.94

2.18

2.37

.39

-.20

-18.16

-2.33

1 .?O

.30

-.30

-14.66

a)

C,:

double

ECT (kJmo1

bond

charge-transfer

carbon

energy pyrazoline)

Diazomethane

HOMO:linear,

LU energies,

so that

have

orbital

been

atom

E ~111.21

the

role

in Table

contrary

the

and

decreased

importance

the

(e.g.

in

r-type

ones:

this

in

electron-deficient

adopted

for

those

and/or

can

provide

some intriguing

conjugated

as

regioisomer

interaction

is

and

distortion

one

sulphones;

detecting trans-phenyl

CN=-.bl

by

styryl

distortion.

of

with

DZM and

ethene

ethene

systematic

are

changes;

on

dipolarophiles

increases

(reduces)

the

which

seems

MO is

increased

“true”

A

substituents,

unoccupied the

the

the

eV Cc= .73

(DZP)

non

(releasing)

i.e. and

electron-deficient

that

than

0.52

index,

enhanced

( ?r-HAO)

in

implies

more

not

undergo

-3.67

pyrazoline)

2-diazopropane

orbitals

3.34

B.

E z-11.19

dipolarophiles), for

regiochemical

B (4-sulphonyl

distorted,

withdrawing

where

a criterion

cases

-22.39 -43.60

increased

electron

cases

-.23 -.40

DB A:

DB_A

-21.90

.35

atomic

behaviour

with

-.37

.39

HO coefficients

systematically

ECT (kJmol-‘1

5

2.59

(DZA)

hybrid alkenes

are

indices

(30°)

0.98

favours

frontier

considerations.

of the

.2b

CN z-.65;

further

in substituted

4.99

adduct

value

1 for

Moreover,

interaction

former

C,

for

diaroacetate

LU coefficients

certain

a negative

c(d)

group;

value

methyl

in electron-rich

reasonable.

sulphonyl

the

for

of HOOP-LUDF interaction

quite

the

eV, Cc=.75,

of

gaps

by distortion;

the

to

between

t

b) The FO coefficients decreased

bound

[ECT B-ECT ,];

energy

reported

%-A

0.01

difference

(3-sulphonyl

Frontier

1

of

HOMOP

Planar Cp

orbitals

candidate

as

importance

LU.

The

sulphone

is

criterion shown

LU

of

a

has

been

in Table

2 as

an example. In the

planar

the

highest

gives

intermediate

CT

charge-transfer LU gains

lower

decrease those

largely, of

the

Apart especially

and

as

Moreover improve

not

to

the

‘X-AO’s

of

the

concerns

aspects the

(LUDp-HODF), application the

correlation

a mixture, alter

in

orbital

planar

involving

between

as

agreement

to

trans-phenyl

the

two adducts. so

styryl

first

LU

By effect become

with

the

but

for

the

of

the

most

experiment.

second-LU

gives

the

distortion,

an lowest

the

important, 17,21

sulphone

The

first

and

its

Table

also

polarizations.

interaction

overlaps

those of

orbitals

the

where

X-HAO’s

coefficients

with

respect

of

reactants.

conclusion

justification

of FO model

the

of

pyrazoline,

whereas

on distortion,

increased

of

of

coefficients

2)

3-sulphonyl

pyrazoline,

of CT energies

due

row of Table

favours

a mixture

higher

out

does

(first

and

favours

increase

some

third-LU

4-sulphonyl

and

points

is

pure from

FO interaction

not

and

energy

distortion

an overall

the

stabilization

energy

index

that c)

CT

energy a

regiochemical shows

calculation

for

b), ignoring

diazcmethane to rate

the

non-frontier

gives interactions

disappointing

results,

and the

alternative

as an acceptor.

DZM cycloadditions constants

procedure

by using

and CT energies

MO’s of as

clearly

distorted

molecules

shown in

Figure

does l.28

164

M. BURDIWJ

et al.

-El7

tJmol-'

qi

Ph

05

Figure

1. Frontier

charge-transfer

rate constants

Total charge-transfer in predictions negligible The

total

agreement

stabilizations

charge-transfer

with log k2

(Figure

with experiment,

Figures

stabilization

for distorted

in

differences

2);

between

As far as regiochemistry not present

thiete

l,l-dioxide

They conform adducts

dipolarophiles]

molecules

(0).

A different

to the common

vs.

nay to gain rigidity

place that all that is

for

diaromethane

B

cycloaddition

to observe

that

shows

an

excellent

N-isobutenylpyrrolidine,

in

to be non reactive.

and

the

total

A

adducts,

is concerned

regioselectvity so

positive

that

the following

indexes

index

i.e.

numbers

the mean

total that

(kJmol-')

regarding

0.33;

PhCH=CHSOjle

CT A

the

is six

in Figure 2, can also be added.

MeCH=CHS02Ph

1.01;

NeCH=CHS02Me

1.11;

PhCHrCHS03Ph

0.32;

0.36. to the experimental

findings,

that is mixtures

for the last three compounds

and A

for the first three.

The analogous

the

molecules).

in obedience

it is interesting

represent

sulphones,

1.00;

and undistorted

(undistorted

stabilization

is reckoned

parentheses

[HO diaromethane-LU

damage.

predicted.

CH2tCHS02Ph

(0)

is to sum up all the interactions,

can be added without

correlation

energies

Ph

dipolarophiles,

plot

but

for

methyl for

diazoacetate

cycloaddition,

N-isobutenylpyrrolidine

and

indicate

a good linearity

N-(l-cyclopentenyl)

pyrrolidine.

for

all The

165

Charge-transfer perturbation model

Figure

2. Correlation

between

total

for the cycloaddition 0 Methyl diazoacetate;

calculated

regioselectivity

to electron-rich respect

In spite

of

as these

to be concluded rate is

that

success

c)

the reactions

calculation

deficient

with experiment.

predicted; (not

of

the

dipolarophiles

The lower

straightforward

theoretical

calculations

are the only examples

would be wrongly

missed;

constants

dipolarophiles.

and B adducts

reactivity

of DZA with

for.

and coefficients),

for all

and rate

Py= pyrrolidinyl

to electron

to agree

a) in DZA cycloaddition,

of enamines;

reaction

reasonable

CNDO/Z energies

deficiencies:

ether

the

accounted

energies to olefinic

0 Diazomcthane;

A adducts

which appears

ones,

to DZII is also

(standard

assignes

charge-transfer of diazoalkanes

fail

falling

results to account

within

involving

dipolarophiles

show that

of

out also

for

the

the left-branch

b) in DZMcycloaddition reported)

application point

falling

fairly

PMD theory

high

of the U-curve, within

the regiochemistry

2-diazopropane

the

some enlightening

this

reactivity it ought region

of ethyl

cycloadditions

the vinyl

proceed

M. BURDISO

166

slower

than

hindrance

those

of

DZM,

whereas

The above shortcomings

the

responsible

ethyl

prediction the

for

U-curves,

calculation;

vinyl

ether

contribution,

these

the

higher

and

Inspection

represent

of Table

DZM,

its

frontier

orbital

differences [6

DZP,

1 appears

If

gaps

energies, Empirical

to reproduce

HO,DP-

governing

29b

it comes

reduction

the empirical

au (4.63-5.44 parameters

tried X=0.20

au

substituted

and X=0.17 Although

The

eV)

(4.63

eV)

relationship

regiochemical

reported of DZM

value,

moreover,

Table

DZP

tends

for

au

weight

of the

both

by

are

is still

alkenes au

to be more

CT stabilization

CH2=CHC02Me

wrong,

8,

to underestimation

of

the

the

decreased

the

overall

HO-LU

to account

decrease

in

MO

the

frontier

between

ionization

to

than

orbital

be

more

those

energy

potentials

suitable

calculated

in the above

to from

calculation,

in the calculated

are

FO energy

3 show

and

eV)

good

than

by the results

ethyl still

interactions;

correct involves

vinyl

whereas

in the

DZA

is

( AE

reaches

reactivity

CH2=CHMe

2 are a

127.68

124.24

122.07

121.92

DZM

139.19

134.27

131.14

129.44

DZP

141.12

135.20

131.85

130.15

eliminated:

positive,

small,

pyrrolidine

sequence reactive.

and

with

DZA;

This

last

are reported.

CH2=CHOEt

DZA

we feel that

above.

N-isobutenyl

reduced)

slight

scatter.

of Figure

less

a

systematic

discussed

still

ethene,

(4.90 eV)

minor

3 where a few examples

number

[X=0.18 au

some arbitrariness,

ether

ranges

we have

with

however,

above

some

unreactive;

the

a large

reacting

au

(5.77 eV),

within

To avoid

the diaroalkanes

location

of Table

fall

au

(often unavailable),

the shortcomings

(-ECT/kJmol-'1

CH2=CH2

values

[X=0.2120

Y

respectively.

the deficiencies

all

one,

DZM

to

always

being

ethene

the X range found

introduced

that

au (5.79 eV) and 0.3047

of X and

non-frontier

within

now a correct

energies

for DZA+

(8.16 eV) for all

corrections

reactive

to be 0.2128

the values

(5.71-6.80

was

a very

EHD,DF1-Y'

use of experimental

N-isobutenylpyrrolidine assume

is not accounted

for

fact,

admitted

contributions,

obtained

and rigid way to overcome in Figure

be

C,,=-0.61).

processes

X and Y amount

olefins

of empirical

should

1) is not sufficient

arguments:

are

which

to

adduct A in the reaction

be due in

resorting

component,

responsible

X, Y could be introduced

frontier

respectively],

can be demonstrated

3. Total

steric

ones:

values

and Y=O.30

N-Cl-cyclopentenyl)pyrrolidine

conclusion

be

differences

that

DZMtsubstituted

both

is a reasonable

the above

out

and/or a systematic

ethenes,

results

favours

counteracted

[e LU,DP -

for mOno and disubstituted au

is

charge-transfer

eV) and 0.21-0.25

the introduction

our choice

the

(5.44

when

In fact,

dipolarophiles

(see Table

the

calculation,

For

of reduction

least

relative

frontier

as a donor;

differences

parameters

Y=O.2606

distinction

their

might

(or estimated)

empirical

Quite similar

and

it

to corroborate

(8.29 eV) respectively.

0.17-0.20

or

DP acts

to DZM + ethene

because

these

and CNDO/Z

(7.09eV)].

at

as an acceptor.

c), on the other hand, can where

1-x

eLU,DF

For DZMt ethene

au

interactions,

than the experimental

energy

underestimated.

of DP acting

underestimation

Shortcoming

of

affinities.

the

experiments,

(HOMODZ,, : CC = 0.75,C,,=-0.65; HOMODZp:CC=0.69,

gaps are rmch higher electron

in

since this contribution

z..O. 11 l,DP-"j,DF'

reactivity

values

found

of DZA with electron-rich

furthermore,

gap in DZP + ethene with respect

coefficient

and

the

of stereochemistry.

other

energy

the contribution

for the high reactivity

for in the above between

of

is

a) and b) can be traced back to an insufficient

Z..lJ. 11 J,DP-"i,DF

interpretation

opposite

29a

is not overhelming.

contribution

the

et al.

Charge-transfer

perturbation

model

9*Log 1

*

3

s

4

167

k,/lmol-‘s-1

0

7

9

9

7

9

_L -%I kJm,l-’

0

=,

Ph [3 171

T

1.lJ40.121.8,

2

I

4

3

Y

9 B*Log

Figure

3.

Correlation

In Table

for

the

0

Methyl

4 the

calculated

to

complete

term

is

experimental

vinyl

ether;

evolution

between

however,

correct

regiochemistry The results

energy

and

with

of

diazoacetate;

energies

diazoalkanes 0

to olefinic

Diazomethane;

of charge-transfer and

the

regiochemistry

the

charge-transfer

(AE

reduced)

and

rate

constants

dipolarophiles.

Py= pyrrolidinyl

energies

regiochemical

k2/l,no,-w

(all

the

(D B_A) from

indexes

ECT values the

refer

frontier

to

the

adducts

approximation

to

the

2)

and

reported.

energy.

interactions,

total

cycloaddition

be favoured),

The agreement the

between

9

regiochemical (column

let

us

even

when it

of column reaction unoccupied

rate.

underline

is

that

represents

1 confirm It MO’s

index

14)

the is

of

from

this a mere

lack

of

dominant with

frontier

dipolarophiles

the

3-4% (column

that

FO interaction only

famous

interaction

correlation

significant the

the

impressive,

3)

the

succeeds of

between

the the

progressive

(columns

(column exception

4-91,

in

total

ethyl

giving

the

charge-transfer

dominant

FO interaction

inclusion while

of

building

of

further up

the

ldule r-Lnarge-rransrer

Frontier -ECT

1

HODZM DB-A

2

LUDF %

interaction

2 ~t""DZM-Uj,DF -ECT

3

4

DB-A

5

CH2=CH2

91.92

CH*=C”Me

77.39

1.67

59

86.66

-0.47

C"2zC"Ph

39.33

5.78

30

83.51

2.46

CH2=CHCH=C"2

55.60

6.60

42

89.27

1.50

analysis

for the reaction

& "0 14 DZM‘- 'j,OF -ECT

6

DB-A

7

68

of diazomethane

I."0 -u. J DZM I,DF -ECT

8

86.66 1.29

olefines.

z .o. -u. I) 1,DZM I,DF

DB-A

-ECT

9

10

91.92

88.17

with

DB-A

-ECT

11

12

92.04 -0.47

86.91

88.17

1.29

88.68

89.27

1.50

89.83

Total

CT DB-A

13

Experimental A%

14

134.27 -0.41

131.14

1.23

87d

1.27

133.28

3.17

looe

1.47

133.96

3.25

lOOf

C"2=C"C02Me

70.04

10.22

50

97.76

5.29

99.06

5.05

99.74

4.79

139.19

4.87

1oog

C"2=C"CN

78.05

6.69

57

95.37

2.62

95.37

2.62

95.88

2.50

136.77

3.36

1009

C"2zCHNO2

47.38

8.68

33

106.68

5.54

106.68

5.54

107.12

5.24

142.70

4.59

67.32

2.87

98.89

2.27

99.66

2.11

99.78

1.96

139.73

1.80

lOOh

98.91

5.08

4.35

0.82

3

C"2zC"OEt

85.04

-3.01

66

85.06

-3.02

85.13

-3.03

85.22

-3.04

85.24

-2.80

129.44

0.54

loo1

MeCH=CHC02Meb

66.08

8.95

49

77.71

4.56

91.09

5.72

93.72

5.49

94.56

5.17

134.27

3.55

1oog

MeCH=C"N02b

47.82

8.37

35

90.23

3.18

101.40

5.30

101.40

5.30

102.08

4.98

137.79

2.75

C"2rCHSO2Ph

PhCH=CHC02Meb

51.77

2.08

39

62.47

6.85

85.31

3.04

93.73

3.95

94.80

3.69

134.40

I.68

PhC"=C"NOZb

49.12

3.72

36

93.69

5.09

98.97

6.15

99.25

4.73

100.03

4.40

135.84

1.75

C"2=CMeC02Ne

66.92

9.69

49

82.50

7.28

93.76

4.01

93.76

4.01

94.59

3.84

136.28

5.38

loom

tkC"=CHS02Phb

5.88

1.01

4

76.17

2.09

86.58

1.40

95.44

3.17

95.66

2.92

135.13

1.07

lOOh

MeCH=CHS02Heb

6.14

1.02

4

79.59.

2.57

89.26

1.94

97.91

3.62

98.14

3.33

137.28

1.19

lOOh

PhCH=C"S02Phb

22.93

0.02

17

46.99

-3.56

89.89

0.37

94.94

1.69

95.35

1.50

135.74

-0.48

4oh

PhC"=CHS02Neb

28.06

-0.18

21

52.85

-3.26

92.03

0.92

97.47

2.02

97.89

1.82

136.73

-0.54

25h

Thiete l,l-dioxide

97.95

-0.03

68

103.30

1.68

104.62

1.60

104.62

1.60

104.89

1.46

144.75

0.15

60q

N-isobutenylpyc

65.17

-5.76

51

65.18

-5.76

66.55

-6.05

77.43

-3.31

77.85

-3.09

127.48

-0.35

-3.27

-3.26

65.77

-3.71

79.34

-4.42

79.73

-4.06

129.62

2.04

N-Cl-cyclopentenyl)pyC

64.46

50

65.33

Mathylfumarate

66.63

48

66.88

100.66

101.11

102.41

139.62

Methylmaleate

65.39

47

65.57

76.97

99.43

100.50

138.34

a) Energy value in RJmol-l; 34; q) Ref. 16

N) *;

c) py=pyrrolidinyl;

d) Ref. 15; e) Ref. 30; f) Ref. 31; g) Ref. 32; h) Ref. 17; i)

Ref. 18; m) Ref.

lOOn

33; n) Ref.

z

Charge-transfer

Table

5.

Percentage

of DP (donor)-_)OF

CH2=CHCO2Me

perturbation

(acceptor)

contribution

CH2iHPh

CH2=CH2

169

model

over

the

total

CT energy.

CH2=CHOEt

CHsCHfle

PyCH=C&)2

OZM

71.6

68.5

66.5

66.3

65.9

61.0

OZA

67.7

64.4

62.3

62.1

61.1

54.7

correlation 0.88,

between

n=9),

destroys

regiochemistry a donor

rate the

according

through

The

inclusion

and

11;

its of

see

13 vs.

14);

interactions

Ref.

the

columns

unified

very

12,

the

Actually,

the

as

of

the

high,

interactions, at

energy

both

meaning

the the

in

the

reaction

summing

only

(log

experimental

up the

k2

it

contributions

vs.

where

does

r2

L.HO J OP-“j,OF’ regiochemistry. In fact

contributions

because

minor

in Table these

of

not

diazomethane

account

(compare

for

columns

= the

acts

the

as

mixtures.

8 and

9 with

10

the

1,3-dipole

with

aspects

shows

are

far

from

reported

in

regiochemistry,

and

Figure

to

be

OP (donor)

this

the

(column

result

of

the

contribution

as

can

be seen

but

they

empirically

OZM (a

adapted,

type

1 and

classical

type

even

because,

necessary.

+

is

satisfactorily

z.. U. JI J ,OZM-“i,DF’ being negligible!

in both

disappear

to

regiochemistry

3 are

between

found

the

that

rate

OZA acts

acts

results

the

as

acceptors.

less

an 35

discussed

of diazoalkane of

13,

as an acceptor,

For

type

also

offer

and

interactions

quantitative

over

the

OZA

where

appreciation,

interactions

a

I1 1,3-dipoles.

1 1,3-dipole)

in OZM, the

a

OF (acceptor)

as

a donor

in OZM cycloadditions,

strong

the

acts

for

the total

CT

5. results,

enamines;

analysis

11 and

) tends

are

with

least

accounts

distinction IOC

acceptor

role

cycloaddition of

on the

acceptor

show

groups

of

than

is

that

larger

only are

at

OZM, but

other

hand,

than

the

reconciled

interactions,

its

expected

level with

allons

the

of the

donor

contribution

contribution for

total

its

to

recover

of

OZA rate

the

reputation

charge-transfer

experimental

one

of

findings; the

chemical

calculations.

Acknowledgment:

We thank

Minister0

Pubblica

della

the

mainly

interactions

qualitative

In conclusion,

moreover,

these

correlations

to

where

as a donor,

columns

contribution

even

e.

gives

diazomethanc

both

an

reported

i.

calculation

11 1,3-dipole

type acts

According is

of

where

of

are

9,

with

unsatisfactory

complete

comparison

treatment

percentages energy

the

Certainly

dipole

column

energies

9).

10 and

(a classical the

to

charge-transfer

agreement

OZM second-HOMO

also

of the

and

overall

HOMO, is

By contrast

from

constants

Prof. lstruzione

R.

Huisgen for

for

financial

sending

us

the

list

constants

and

support.

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7. K.N. Houk, A. Bimanand, Heterocycles,

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"1,3-Dipolar

Reissig,

and

H. Huber,

H.-U.

Reissig,

Cycloaddition

with phenyl and

vinyl

trans-phenyl,

respectively, yielded

by

q7in

results

sulphone styryl

agreement Careful

different

conditions

of detectable

investigation.

Full

Berlin,

results

the

added

of products.

of

adducts

for each dipolarophile

bases)

L.J. Luskus,

R.

Huisgen

that

for

allowed

in

trans-n-dodecyl DZA

and

excess

The structure

40:60, sulphone propenyl

styrene,

n-butyl

results

reacts

sulphone

and

propenyl

us to rule out

products

DZM

styryl

(A:B=25:75

between

of DZA with

molecule.

b)

trans-methyl

reported

reaction

One of the dominant

results will be published

330;

we confirmed

mixtures);

previously of

18,

A and with trans-methyl

mixtures

reaction

analysis

Data of Free Polyatomic

the

under

formation

vinyl

ether

at

from the reaction

of these compounds

is under

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Molecules",

1973, 95, 7301.

Hellwege

and A.M.

Hellwege,

Springer,

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to

NMR

1979,

1984, vol. I, p. 135.

in particular

of adduct B. The cycloaddition

95°C gave rise to a mixture of two DZA molecules

controlled;

of the crude the

and

(solvent,

amounts

1979, 101, 3647.

ed. A. Padwa, Wiley,

were

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TLC

J.Am.Chem.Soc.,

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Chemistry",

21. Some of the regiochemical

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H.-O. Martin, C.

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1970, p. 250.

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various

J.K. George,

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dipolarophiles_,require

energies

to

reach

equivalent

CNDO/Z) is linearly correlated to log k kJmo1 (e.g. for DZM): the result is quite rea%onable for Cr=30° log k = -0.18 Edis + sa5.13, n=B,'r=O.BB (notice that low iis@ rtion energies correspond to high rate constants) and conforms to recent

distortions;

distortion

conclusions

to

investigation, itself finding

about

of ours

cyclobutenes

energy

explain

only

the comparison

anti/-

distortion

exists

(E

energy

because

the

is, for now, a by-product

29. a) R. Huisgen

in "1,3-Dipolar

143; b) ibid.,

of *

and anti

stereoselectivity cannot n

of

distinguish

reactions

considered

DZM

deformations

in

cycloaddition.

between give

regioisomers the

same

cis-disubstituted

Although

type

(the of

deserving correlation

adduct);

this

of our study.

Cycloaddition

Chemistry",

ed. A. Padwa,

Wiley

1984,

vol.

1,

p.

p. 111.

30. P.K. Kadaba, T.F. Colturi, J. Heterocyclic Chem., 1969, 829. 31. R. Huisgen, A. Ohta, J. Geittner, Chem. Pharm. Bull., 1975, 23, 2735. 32. T.L. Jacob

in "Heterocyclic

33. A. Ledwidth, 34. J. Bastide, 35. A similar frontier

Compounds"

D. Parry, J.Chem.Soc.C. O.Henri-Rousseau,

conclusion interaction

was

L. Aspart-Pascot,

reached

energies.

Ed. R.C. Elderfield,

Wiley,

New York,

1957, Vo1.5,

p.72.

1966, 1408.

by Huisgen

Tetrahedron, 1974, M, 3355. 1, vol. 1, pages 132-135)

(Ref.

on

the

basis

of