Absolute rate constants for the additions of halophenylcarbenes to alkenes: a reactivity-selectivity relation

Tetrahedron Letters,Vo1.24,No.48,pp Printed in Great Britain

ABSOLUTE

RATE CONSTANTS TO ALKENES;

FOR THE ADDITIONS

b

aDepartment of Chemistry, Rutgers, New Brunswick, New Jersey 08903 Department of Chemistry, Columbia 10027

the relative

rates of their cycloadditions

flash photolytic activation

techniques

parameters

to the addition

of New Jersey,

New York, New York

they provide

its general

occurrence

Halophenylcarbenes flash photolysis isooctane

to various

variation

reactions.

for a "normal" Although

- &

solutions;

eq. (1).

bromite

or hypochlorite

obtained

by the action Appropriate

rines 1 in alkenes

oxidations

of benzamidine,5

of molten n-Bu4N+F-

cyclopropanes (A), and were

4 were

identified

whereas

(containing

isolated

and &

are important in

study.3

(A>300 nm) or

in alkene or alkene/ were prepared

fluorophenyldiazirine

0.1 equiv.

con-

of carbenic

correlation

by hypo-2a was

of H20) on neat -lc at

from steady state photolyses

by standard

5313

-la - & E

data which

in our Hammett

by steady state photolysis

Bromo and chlorodiazirines

correla-

has long been assumed,l

and it was not observable

(he, = 351 nm) of 3-halo-3-phenyldiazirines

Hammett

The new results

reactivity/selectivity

and

the new

of the dependence

such a relationship

were generated

applied

and have obtained

carbon.

nanosecond

rate constants

Here, we report kinetic

-at the carbenic

is controversial4 &

of absolute

by direct measurements,

from studies of

Now, however,

We have previously

of ClCPh with alkenes,2

obtained

of carbenes

a1kenes.l

the direct measurement

clear evidence

addition

and selectivity

of a series of E-X-PhCC1.3

on substituent

carbene/alkene

25°C.6

University,

a*

Robert A. Moss,

The State University

cycloadditions.

reactions

the first examples,

reactivity

permit

for carbene

tions for the additions

because

b

The absolute rate constants determined for the additions of FCPh, ClCPh, and BrCPh to Me2C=CMez, MepC=CHMe, trans-MeCH=CHEt, and n-BuCH=CH2 appear to follow a reactivity/selectivity pattern of the "normal" (inverse) type.

Much has been learned about the reactivity

stitute

RELATIdN

Nigel P. Hacker,

b

methods

OF HALOPHENYLCARBENES

A REACTIVITY-SELECTIVITY

D. Phillip C~X,~ Ian R. Gould, and Nicholas J. Turrob*

Summary.

0040-4039/83 $3.00 + .OO 01983 Perqamon Press Ltd.

5313-5316,1983

techniques.

2,7_10

of diazi-

5314

Rl

Ph

R2

hv

-1

-2

a,

R1=R~=R~=R+v,~

b, X=Cl

b, X=Cl

a,

R1=R2=R3=Me,

5, X=Br

2, X=Br

2,

R1=Me,

2,

II1 =~f-Bu,

5,

X=F

X=F

2,

Flash photolytic ClCPh.2

studies were carried

Each carbene

and its uv spectrum sient spectra or benzene

of the same carbene

solutions

at 23'C.

These

The spectra

are seen to be blue-shifted

order

is that expected

gens.12

The effect

The transient quenched

absorptions

tions of quencher,

as one proceeds

bimolecular

correlations

isooctane

to FCPh.

effects

from ClCPh

of sufficiently

The

of the halo-

to FCPh. were

high concentra-

was found to be pseudo-first-order.

of the decay rate constants

rate constants

tran-

(77 K, 23'C) in nm

carbenes 2 in isooctane

absorptions

at 77 K

FCPh, 270 ~300 (isooctane)."

and mesomeric

In the presence

the decay of the transient

matrix

in aerated

X,,, values

as one proceeds

of laser flash generated

for

with point-by-point

from BrCPh to ClCPh

mix of inductive

of alkenes -3a - 3d.

The slopes of the linear tions provided

was obtained:

pronounced

developed

in a 3-methylpentane

307, 310 (benzene);

for the differing

is particularly

upon addition

ClCPh,

generated

by laser flash photolysis

Good agreement

328, 330 (isooctane);

R2=R3=H

R2=R3=R4=R

spectra were compared

generated

were BrCPh,

R4=Et,

out in accord with procedures

was first photolytically

was determined.

R4=B

versus

(Table 1) for the reactions

alkene

concentra-

of carbenes

2 with

alkenes -3.12a As deduced

from the stereospecificity

carbenes -2a - 2c react with simple alkenes constants (&)I

(Table 1) is more than two orders

to the smallest

lute reactivity

order

based on anticipated singlet

carbene

[(.a) + (a)]

2p orbita1.l

as singlets.7y8.13 of magnitude;

rate constant

is Br > Cl > F, which halogen

of their additions

The overall

With each alkene,

stabilization

as measured

span of the rate

the ratio of the largest

is the inverse of the carbene

lone pair resonance Moreover,

is -400.

to cis- and trans-butenes,

by the "spread"

+

the XCPh abso-

stability

of an adjacent,

[(&I

order

vacant,

or ratio of the largest

5315

Table

1.

Absolute

rate constants

for additions

of XCPh to alkenesa

Carbene

, FCPhb

Alkene

t

CICPhC

BrCPhb

Me2C=CMe2

1.6

x lo8

2.8 x lOa

3.8 x lo8

MezC=CHMe

5.3

x 107

1.3 x 108

1.8 x lOa

trans-MeCH=CHEt

2.4

x 106

5.5 x 106

1.2 x 107

"-BuCH=CH2

0.93

x 106

2.2 x 106

4.0 x 106

0.83

0.70

d

0.89

%XY "spread ,,e

172

127

95

aRate constants are in L/mol-set and were determined in alkene/isooctane solution at ky laser flash pptolysis. Reproducibilities are <*lo%. See text and ref. 2. bThis From ref. 3. Carbene selectivity index determined at 25'C by relative reactivity scale , ECCl, = 1.00. See ref. 1, first citation. eRate constant ratio for additions Me2C=CMe2 vs. n-BuCH=CHz.

23OC work. studies; to

(Me2C=CMe2)

over

the common

to smallest

set of alkenes

is identical comparative

relative

"normal" cularly

of absolute

reactivity

type.4

cycloadditions

studies

indices

(m -CXY'

(Table 1) thus provides

direct evidence

and selectivity

reactions,

and interpretation

remain controversial,4

on theoretical

it is of particular afford

This order

1) derived

for an inverse

grounds

interest

correlation

to note that the reactions

data.15

Thus, with any given alkene,

CF is the least reactive

carbyne,

whereas

(greater

"spread")

discrim-

relationship of the

of such relationships,

and should be "normal"

from

= 1.00.1

with carbene/alkene

their occurrence

rate constant/carbyne/alkene

CF is more selective

see Table

or a reactivity/selectivity

the significance

(CF, CCL, CBr) with alkenes

of alkenes.15

of the carbenes

of XCPh and CC12 on a scale where m -Cc12 rate constants

is expected

In this context,

selectivity

carbene/alkene

Although

in solvolytic

the selectivities

also follow the inverse order, FCPh > ClCPh > BrCPh.

reactivity

(selectivity)

of absolute

rate constants,

to that of the carbene

The comparison ination

(BuCH=CHz)

parti-

in carbene/alkene for halocarbenes.14 of halocarbynes

data similar

to OUT carbene

and CBr the most reactive

than CBr over the available

set

5316

Activation mined,

parameters

and closely

These parameters

resemble

for the additions the reported

and their interpretation

Acknowledgment.

We are grateful

of &

values

and -lb to &

and z

for the additions

will be discussed

to the National

have also been deter-

of b

to these alkenes.'

at length in our full report.16

Science

Foundation

for financial

sup-

port.

References

and Notes

(1) R. A. Moss, Act. Chem. Res., 13, 58 (1980); R. A. Moss in "Carbenes," Vol. I, eds. M. Jones, Jr., and R. A. Moss, Wiley, New York, 1978, pp. 153ff.; R. A. Moss and M. Jones, Jr., in "Reactive Intermediates," Vol. 1, eds. M. Jones, Jr., and R. A. Moss, Wiley, New York, 1978, pp. 69ff.; Vol. 2, 1981, pp. 59ff. (2) N. J. Turro, J. A.-Butcher, Jr., R. A. MossTW. Guo, R. C. Munjal, and M. Fedorynski, J. Am. Chem. Sot., 102, 7576 (1980); N. J. Turro, G. F. Lehr, J. A. Butcher, Jr., R. A. Moss, and W. Guo, J. Am. Chem. Sot., 104, 1754 (1982). (3) R. A. Moss, L. A. Perez, N. J. Turro, I. R. Gould, and N. P. Hacker, Tetrahedron Lett., 6, 685 (1983). (4) C. D. Johnson, Tetrahedron, 36, 3461 (1980); G. W. Klumpp, "Reactivity in Organic Chemistry," Wiley, New York, 1982, pp. _. 219-222, 352-372. (5) W. Ht.Graham;.J. Am. Chem. Sot., 87, 4396 (1965). (6) R. A. Moss, D. P. Cox, and J. Terznski, J. Am. Chem. Sot., in press. Diazirine k was characterized by ir, lH, lgF, and 13C nmr, and uv spectroscopy, as well as by photolysis Spectroscopic and preparative details for & in alkenes to afford known FCPh adducts. are included in the manuscript in press. 2220 (1969). (7) R. A. Moss, J. R. Whittle, and P. Freidenreich, J. Org. Chem., 2, (8) R. A. Moss, Tetrahedron Lett., 4905 (1967). (9) R. A. Moss and J. R. Przybyla, Tetrahedron, 25, 647 (1969). for Dhotolvtic preparations of the (10) We thank Dr. J. Terninski and Mr. W. Lawrvnozcz adducts of 2c with 3c and 3d and of 2a wi;h 3b - 3d. . I . . (11) The transient spectrum of EPh couldnot be determined accurately below 300 nm because of interfering absorption by the diazirine precursor; good agreement between low and room temperature spectra was obtained in the spectral region above 300 nm. (12) J. N. Murrell, "The Theory of the Electronic Spectra of Organic Molecules," Wiley, New York, 1963, pp. 189-237. (12a) Available data'y13 permit comparisons of the ratios of absolute rate constants for carbene additions to Me2C=CMez vs. Me2C=CHMe (Table 1) with analogous classically determined' The data are (Labs ratio, lcrel): 3.0, 3.113 (competition) relative rate constants. With reproducibilities of *lo% in lcabs (FCPh); 2.2, 1.6 (ClCPh); and 2.1, 1.8 (BrCPh). (*14% in the ratios), the agreements are reasonable. (13) W. Lawrynowicz, unpublished study of 2a generated from @. (14) W. W. Schoeller, Angew. Chem. Int. EdFEngl., 0, 698 (1981); N. G. Rondan, K. N. Houk, and R. A. Moss, J. Am. Chem. sot., 102, 1770 (1980). (15) B. P. Ruzsicska, A. Jodhan, H. K. J. Choi, 0. P. Strausz, and T. N. Bell, J. Am. Chem. c., 105, 2489 (1983). (16) A full paper is being prepared for a symposium-in-print issue of Tetrahedron to be devoted to carbene chemistry and published in 1984. (Received

in

USA

22

August

1983)