Studies on structurally simple α,β-butenolides. III.

Ttrmhrdron Vol 19. No 3. pi 395 10 4X. Pnntcd ,n Great Rr~ln~n

co4o4320/83/0303%-0613 al/o Perpmn Press Ltd

1983

STUDIES ON STRUCTURALLY BEHAVIOUR OF (-)-(s)+HETEROSUBSTITUTED

SIMPLE 3,BBUTENOLIDES.

III.

y-METHYL-o,@BUTENOLIDES

TOWARDS NUCLEOPHILES.

PROTOANEMONIN AS INTERMEDIATE IN AN ELIMINATION-ADDITION

MECHANISM.

*

, R.M. Ortuiio and 0. Ponsati

P. camps+, J. Cardellach, J. Corbera, J. Font

Departament de Quimica Organica, Facultat de Ciencies, Universitat Autonoma de Barcelona, Bellaterra. Barcelona, Spain.

Abstract.- The reactivity of the title compounds with different nucleophiles has been checked and it was shown that products from reaction with sodium phenylthiolate result from an elimination-addition process in which protoanemonin is the key intermediate. The synthesis of (-)-(RI-bangellca lactone is reported for the first time. -

In part cently

II of this series', we have re-

reported

synthesis

the

of

active Y-methyl-o,b-butenolldes leaving groups tion, namely

optically

as substituents

thyloxol-3-en-2-one,

1, and (-j-(2)-53. Attempts

of the other

the

molecule,

We

have

studied

allylic

the reactivity

us to propose

of these

found

of

by

mecha-

(CH2C12/CN-)

conditions.

On

3 with KCN

the

under

other

phase

hand,

tives of

y-methyl-a,&butenolides

of mesylate basic

&nitrogen

z

and

nitrogen

phthalimide,

like

some

yielded

only

Michael

by

llowed

by

basic

protoanemonin

Once

this

product

nucleophiles

+

philes

cannot;

reacts

giving

te

Facultad

de

Universidad

de1

Pafs

Vasco,

Alza.

Quimica, San

Sebastian,

( f 1-2 was of

or weakly

only

now

ob-

unchanged

Quimica

395

reaction

on

(on11 halides react giproducts).

elimination giving

Ahe" Y

fois a

protoanemonin

is formea,

only

4. -

very soft

(e.g. PhS-) can give 1,6-conjuga-

addition product

or, as is well 2 rises .

Spain.

of the allybasic nucleo-

performed

substitution Y-

group,

4 as the main crude component.

Organica,

not

1 eq. of PhS- under

recovery

fastest

rapid

leaving

de

the

ving the expected

good

Departamento

presence

of PhS- to di-

that abstraction

the

is

aside

address:

with

the title substrates,

deriva-

Present

is explained

adduct

However,

lit proton

by reaction

pyrrolide,

(' )-2,

(15 %) during the reaction.

operating

We believe

iodide 3 with very weakly

anions

we

20 % of unaltered,

dimerization

disulfide

philes

prepare

nucleophile

mechanism.

5, as the only isolated product,

to

this

1, 2, 3 or 5 gave us the clue for the proposed

of

formed in very low yield. Attempts

product

the oxidative

in methanol gave methyl 2-methoxy-

4-pentanoate,

last

tained.

transfer

reaction

With

yields of reaction products:

(+_I-?, together with

this

and

4 was the only product

or

1.

good

argon, the starting material was not recovered

detected when the reaction was done in heterophase

Table

In fact,

of tosylate 1 and iodide 2 with

protoanemonin

with

by the use of a 5 % defect of PhS- but also

ion did not give the desired nitrile.

Instead,

or

on

have

phenyl

cyanide

new

optically pure, starting material.The

nism. Reaction

anion

(1, 1 and -3) as well (-)-(S)-5-bromomethyloxol-3-en-2-

6, have been studied and the results are

given

one,

proton.

a unified

phenylthiolate

substrates

and 81 ( ? )-3-phenylthio-5-phenylthiomethyloxolan-2-

with several weakly basic nucleophi-

allowing

les,

now

the

basic

!Gphenylthiomethyloxol-4-en-2-one,.

functional groups present

mainly

the

of the very strong nucleophile

( t )-5-phenylthiomethyloxol-3-en-Z-one,

to preon these

were fruitless due to the competiti-

in

compounds

as one,

1, (-)-(S)-5-methanesulfo-

iodomethyloxol-3-en-2-one,

weakly

the mentioned

at the &posi-

pare ether derivatives by SNjreactions

veness

and

possesing good

(-)-(S)-5-p-toluenesulfonyloxyme-

nyloxymethyloxol-3-en-2-one,

substrates

Reactions

in

(a), while other nucleo-

this

last

open-chain known,

case,

compounds

dimerizes

4

either

(e.g.

2)

and polyme-

P. CAMPS

3%

et al.

Table 1

ExperimentCa)

eq. PhS-

Substrate

Y

% yield (b)

ReactIon time

Molar ratlo (')

0

tr+ Xr

Starting material

( 9-z

8

( 9-z

(1)

Y=Br,

6

0.95

14 h

55

1.6

1.0

3.8

0

(2)

Y=I,

2

0.95

14 h

62

0.3

1.0

0.5

0

L3)

Y=TsO, 1

0.95

14 h

69

1.0

1.0

2.0

0

(4)

-1 -1

0.95

lh

67

1.2

1.0

1.4

0.95

10 min

60

0.6

1.0

0.9

(6)

1

1

10 min

63

0

1.0

0

0.3

(7)

Y=Mso, 2

14 h

46

--_

1.0

0.1

0.2

(5)

(8+d'

0.95

4

(9)(d) (10)(d)

;

0

,

0

catal.

10 min

64

0

1.0

0

4.0

catal.

2.2 h

64

0

1.0

0

4.0

_--_-_

10 min

--

lTC0”.

0

0

0

(a) Only the experiment (6) was performed under argon atmosphere. (b) Calculated

from the equivalents

of added PhS-, except in experiments

(8)-(10) where it was

calculated from PhSH. (c) Calculated on the basis of isolated products

(column chromatography),

except in experiments

(lo), where it was calculated from the PMR spectrum of the crude reaction mix-

(4), (9) and ture.

(d) In the presence of 1 eq. of PhSH.

In agreement with the r61e of protoanemonin as intermediate,

4

(prepared independent--

tlon

(PMR control) were detected,

poor

nucleofugacity

ly3) was made to react with 1 eq. of PhSH and B catalytic amount of PhS- in the conditions shown

in Table

nixture

of

To our

knowledge

(2 j-7 and

1,6-addition

a 64 % yield of a

1, giving

to

in a 1:4 ratio.

(?)-s

this

The ratio deconjugated,

reaction

of

the

conditions.

PhS-

pair In

(?)-z,and

depends upon the PhS-/PhSH

fact,

in

the

( t)-z is the

more stable and is quantiia-

or when e is allowed to stand in

a silica gel column over,

reaction

of

for several hours. Moreg

with

the

enol

ring

opening

both

silica gel and e-TsOH

of

of

e-TsOH

results

lactone.

in

However,

let optically

ac-

of

PhSH

over

to the concentration .of the

(Scheme 1 summarizes the pro-

posed mechanism).

.

conjugated,

The base butenolides

a

and

trident

diate.

the

had earlier

systems, thy1

catalyzed

to

isomerization

corresponding

for 5-meA , and

5-tert-butyloxol-4-en-2-one anion

was

postulated

as

In our- case, PMR hrovlded

a hydroxyfuran

anion

= 6.6 Hz),

tem, JAB

(6

3.5 and 6.7, AB sys-

when

the

c:>ectrum of a

solution of a mixture of (!)-2 end c in DKSO-d6 containing

1 eq. -t-BuONa, was recorded. In fact, such an anion can be the intermediate in rhe conjugation of 8 to (+I-7 - in basic media. the sulfur derivatives ( + j-7_

tion carried

tions (polarlmetry and PMR control).

cell) but

neither double bond deconjugation nor elimina-

Interme-

zvidence of

Nevertheless,

in a polarimeter

of f3,~-

conjugated

been reported

tive 7 unaltered and treatment with catalytic PhS- showed instantaneous racemization (reacout

group.

(? j-2 results unambi-

(?I-7. ( 21-9 in the reaction mixture

pair PhS-/PhSH.

tively obtalned from 8 by treatment with catalytic

amount

addition

although siml-

between

thermodynamically

The

catalyzed

protoanemonin,

8, butenolldes

concentration

base

is also sensitive

have been recently reported 5

due to the

phenylthio

gously -as has been indepently verified- from

first reported

lar 1,6-additions

the

The Michael adduct

is the

with other y-iliden-C$ Bbutenolides

of

and 8 are completely stable in neutral condi-

We

have synthesized,

as far a: we know,

Studies on structurally

0

PhS-

l

' +‘

397

simple a$-butenolides-III

PhS- ,

'""e

PhS-

-HY -4

Y = TsO, 1 MsO. 2 I. Br,

+

PhSH

3

-

6

PhS (+)-2

Scheme 1

for the first. time, 2-one,

lo,

tone),(by pyrolysis

(S)-5-phenylthiomethyloxol-3-en-2-one,

(-)-(R)-%nethyloxol-3-en-

(optically

active b-angelica

lac-

have been synthesized

of 2,3-O-ethoxymethylene-5-

deoxy-YE-ribonolactone,

17) and it

does

bonolactone.

not

we can

Therefore,

equilibrium

for

pare 0;

alternative

optically

lactone, 12, and 5-deoxy-2,3-g-ethoxymethylene5-n-propylthio-Y-g-ribonolactone,

does not

(Scheme double

of

2) prior bond

by

the

13,

respec-

tlvely. route

6 -sulfur

y-methyl-a,B-butenolides

substitution

5-deoxy-

conclude that a tauto-

synthetic

active

in good yield from D-ri-

through the orthoesters

these systems

exist in neutral media. The

and

2,3-G-ethoxymethylene-5-phenylthio-y-IJ-ribono-

racemize In neutral conditions.

merlc

1

(-)-(S)-5-~-propylthiomethyloxol-3-en-2-one,~,

group

to the creation pyrolysis

of

the

of

anions

gave

-11 with pyrrolide unidentified pro-

ducts. Thus, the synthesis of

in the in

reaction

or phthalimide

derivatives

consisted

tosylate

However,

to pre-

Y-methyl-a,&butenolides

11

The enantiomeric

of the C-C

1, 1, 3, 5, I, g

orthoester,

purity of the compounds

and 14 has been established

by chemical correlation with the known (t)-(R)-

method described by us in part II'. Thus, (-)-

5-methyloxolan-2-one, 15".

RS

0

H' -0=_

US-

RS

-x2= 0

H'

R=PhS.

1

/ R=Ph,

1

12

R = q-Pr, 13

111111

c

'Q"

_

,

.

d

’

x”

2) H2, Pd/C

H

R = I, R=H,

6-lj-substituted

is still unsolved.

OEt

16 17

Scheme 2

10 -

\

P. CAMPS

398 EXPERIMENTAL PART

d

ai.

(two t, 5.7.3; 3H); 3.20-3.40 (complex abs, 2H) 3.60

and

3.64

(two q, J=7.3;

2H); 4.55-5.15

(complex abs, 3H); 6.00 (s, 1H) and 7.25-7.65 M. ps hot

have

stage

tions

and

were

P-10

been

determined

are uncorrected.

obtained

on

a

on

rota-

Bellingham-Stanley

Distillation

polarlmeter.

a Kofler

Optical

of

small

a-

mounts were effected on a rotational distillaKRV

tar B&hi,

Mod.

oven

given).

temp.

65/30 MS

with a Hewlett-Packard

(only external or

spectra

were

apparatus,

recorded

model

5930A

working at 70 eV. The II?spectra were recorded on

a

Per-kin-Elmer

Spetrophotometer,

(complex

abs, 5H); IR (film). 3100, 3020, 2970,

1790,

1480,

1435,

1340,

1250,

1170,

1100, 1060 and 1020 cm-l; MS, m/e (%) 296 CM+, 11). 251 (47). 222 (20), 187 (15). 176 (12), 174

(17),

(1001, 77

173

(12),

(71, 109

110

(32)

and

45

160

(9).

159

(19), 79

(80).

(7), 123

(9). 78

Found:

5.25; S, 10.50. C14H1605S

C,

(201,

57.01; H,

requires: C, 56.74;

H, 5.44; S, 10.82 %.

model

720. The PMR spectra were recorded on a Per-

1580,

A

10

ml

flask,

containing

12

(3.02 g,

10.2 mmol) was connected to a rotary microdls-

kin-Elmer Spectrometer, model R-12 A; chemical

tillation

shifts

for 2 hr. Then, the ethanol formed during the

are

given

in

ppm

relative

to TMS (6

apparatus

and heated

at 220Q/l atm

pyrolysis was eliminated -in vacua to give 1.53 g of a residue, which chromatographed through

scale).

!-)-(S)-5-bromomethyloxol-3-en-2-one, A solution of 1 lithium

bromide

of

DMSO

anh

(400 mg,

was

30 g of silica gel, using hexane-ethyl acetate

5

(250 mg, 0.92 mmol) and 4.62 mmol) in 1 ml

magnetically

stirred

for 3

(9:1), afforded 1.03 g of 1 (49 % yield). E.p. 160Q/14 torr;

[a] F=-34.48Q,

(CDC13), 3.00

PMR

c=O.58 in CHC13.

(dd, 5~14, J'=8;

hr at 60Q. then diluted with 4 ml of H20 and

(dd, J=14,

extracted

(dd, 5~6. J'=1.7; 1H): 7.14-7.65

were

with

washed The

Na2S04. pressure

ether.

with

through

silica

to give 5

brine

solvents

and

The

combined

and

extracts

dried

with

anh

were removed at reduced

the

residue

gel,

using

chromatographed

CH2C12

as

J'=5.3;

1H);

5.14

1H); 3.45

(m, 1H); 6.11 (complex abs,

6H); IR (film), 3100, 2950, 1750, 1600, 1580, 1480, -1

Cftl

1440,

;

1320,

m/e

MS,

(%)

1160.

1060

and 1020

206 CM+, 7), 154

1100,

(4), 126

eluent,

(71, 125 (7.51, 124 (11). 123 (1001, lid (12),

(120 mg, 74 % yield) as an undisti-

109 (28). 85 (191, 84 (161, 83 (30), 79 (161,

ta1;0=-150Q, c=2.94 in CHCl 3' (CDC131, 3.70 (m, 2H); 5.37 (m, 1H); 6.34

llable liquid.

78 (121, 77 (22) and 45 (43). Found: C, 64.28;

PMR

H,

(dd, 5~6.0, J'z2.0;

1H); 7.67 (dd, J=6.0, .I'=

5.02;

1.4; 1H); IR (CHCl3), 3050, 1780, 1610, 1330, -1 1160, 1030 and 895 cm . Found: C, 34.29; H, C5H502Br

2.94.

requires:

C, 33.93; H, 2.84%.

S,

15.79.

CllH1002S

requires:

C,

64.05; H, 4.88; S, 15.54 %.

(-)-(S)-5-n-propylthiomethyloxol-3-en-2one.2 Diastereoisomeric

5-deoxy-2,3-O_ethoxfle-

o-(S)-~phenylthiothyloxol-3-en-2-one,

thylene-5-n-propylthio-Y-_D-ribonolactone, 13, was prepared from 11 and Na(n-Pr)S (from

To a stirred

n-PrSH and NaH) -

7 and ice-cooled solution of

2,3-c-ethoxymethylene-5-0-tosyl-y-D-ribonolactone, 11; (4.01 g, 11.2 mmol) in 20 ml of anh a solution of NaPhS, prepared

DME.

from PhSH

above.

(CDC13),

0.80-2.00

(t, J=6.7;

and NaH, (1.48 g, 11.20 mmol) in 20 ml of anh

3.66

(two

DME

abs,

3H)

was

llowed washing

added

slowly

and the mixture was a-

to stand at 4@ for 14 hr. Filtration, of

the

solId

with

30 ml

of anh ,DME

in 69 % yield, by the method

described

2950,

2H);

B.p.

2.92

q, J=7.3; and 6.00

2900,

1780,

150Q/0.05

(complex

(d, J=4, 2H);

8H);

PMR 2.60

2H); 3.62 and

4.57-5.20

(s, 1H); IR 1450,

torr.

abs,

1370,

(complex

(film), 2990, 1350,

1300,

1250, 1180 and 1060 cm-I; MS, m/e (%I 262 CM+.

and evaporation of the solvent at reduced pres

231,

sure,

chroma-

179 (lo), 177 (38), 175 (221, 147 (loo), 145

hexane-

(32), 144 (191, 143 (43). 129 (391, 101 (25).

afforded 3.2 g of a syrup, whi@

tographed

through

silica

gel

(3:2

CH2C12) yielded the diastereoisomeric 2,3-pathoxymethylene-E-phenylthio-y la&one. b.p.

E-deoxy-

-g-ribono-

12. (3.02 g, 91 % yield) as a syrup,

160Q/0.2

ton’.

PMR (CDC13), 1.15 and 1.24

217

(581, 189

(6), 188

(5). 187

(17),

89 (31) and 68 (12). Found: C, 50.62; H, 7.18; S,

11.97.

C11H1805S

requires:

C,

50.36;

H,

In a similar way as above, pyrolysis

of

6.91; S, 12.22 %.

Studies on structurally E

at

243",1

of' the

atr.. followed through

crude

10

by chromatography

for

silica gel, using

obtained.

(a:11 as

gel.

g of

lllxture :':‘CH2C12-hexane

a

aff\-rded -14 in 73 % -71 tc '_' ; :cr: =-87.3Q,

D

iC@C;,), plex

1.0

abs,

J'=1.8;

1H);

(film), 1380,

130

5.2

7.62

3100,

1330,

MS , m/e,

c-1.18

in

(m, 1H);

2990,

100~10.02 CHCl

2950,

1160.

6.24

2900,

(corn-

(dd, J=6,

J'=1.3;

1100

1H); IR

1760,

and

PMR

3'

1460,

1020 cm-l;

172 CM+, 121, 145 (I), 144 (11,

129

(5,.5), 89

B.p.

(dd, J=6,

1240,

(%)

(21,

yield.

eluent,

(t, J--7.3; ZH); 2.75-3.20

2H);

simple +butenoiides-Ill

(2.51,

113

(loo), 85

(21,

101

(141, 83

(15), 97

(171, 61

(601,

55 (34) and 43 (61). Found: C, 55.65; H, 6.91; 18.70.

S,

C8H1202S

requires:

55.78;

C,

H,

7.12; S, 18.59 %.

Reaction

of

(-)-IS)-5-e-toluenesulfonyl-

oxymethyloxol-3-en-2-one, tion of

I, vitb NaPhS: obten-

30 min,

a

1

(840 mg.

a

solution

with

stirred

and

3.14

mmol)

of

yield)

(dd,

and

g

75.5-76.50.

J=18.7,

J'=8;

J'=6.7;

of

PMR

lH),

NaPhS

ice-cooled solution

(q. J=5.3; (CHC13),

1Hf; 7.4

3050,

(41,

combined The

pressure

was

136

(22 % 2.50

[dd. J=18.7,

(complex abs, 1590,

(2), 206

(41, 135

10H);

1490,

1445,

(%I 316 lM+,

(51, 147 (5.5),

(5).

125

(11.51,

124

(421, 101 (9)‘ 99

(101, 97

(ll), 96 (17). 91

(12)‘ 79

(251, 77

(35). 69

(32), 65 f31), 55

(311 and

45

10.13.

S,

(46). Found: C, 64.52; H, 5.13;

C17H1602S2

requires:

C, 64.52;

H,

5.09; s, 10.11 %.

Reaction To

in 45 ml of anh DME,

(390 mg,

a

extracted

organic

2.98

mm011

were

in

4

640

9:l mixture afforded

diluted

Na2S04

hexane-ethyl

gel,

acetate

to

with

anh

which

stand

CHC13

organic

and

the

at 0'

and

liquors volatile

materials

The PMR spectrum ture of

active the

were 2H);

3.70

7.59

(complex

2950, -1 cm .

1805,

only

were

identical to those of spectroscopic

The

following: (m,

2H1;

abs,

5H); 1590,

experiments on Table

PMR

(CDC13).

5.26 IR

(CHC13),

W-U

(11,

(2),

3050,

1440 and 1100

(31,

(41 and

1, were carried out

in

and

(C.99 g,

as before, but under argon at-

10 mmol)

(2.0 g.

10 mmol)

was

stirred

the catalyst

of abs EtOH, taking care dry.

torr;

The

and

15

the

(178

mg,

{o)f=+27,

with

removed

residue 63

for 2 hr., then

washed

25 ml

of the solid becoming

was

solvent

105*/35 tori-,

3020,

was

% yield).

at

reduced

distilled B.p.

to

1100/18

c=1.33 in CH2C12. (Lit6, b.p. {u};=+30.1.

~0.85

in CH2C12).

and NaPhS

in 130 ml of anh DME at Oe

abs,

4H)

2950,

and

1780,

4.51 1460,

(m, 1H);

IR

1420,

1390,

(film), 1350,

1200, 1180, 1125, 1100, -1 1060, 1000 and 950 cm . Found: C, 59.82; H, 1300.

1

(I.5 gf were added to a solution

the mixture

filtered

plex

from

from 3.

PMR (CDCl,), 1.47 fd. J=6.3; 3H1; 1.6-2.7 icom-

(?l-3-phenylthio-!&phenylthiomethyloxolan-

mosphere,

15.

(400 mg, 4.76 mmol) and

and

(m,lH); 7.16-

1480,

Raney-Ni

NaHC03

3.18

a similar way as described above.

a-one, (21-g. Operating

the

of 3 (632 mg, 2.82 mmol) in 10 .ml of abs EtOH

give

(71, listed

as

data

pressure

The

ratio,

products.

148 mg of recovered star-

7.

1800,

evaporated

of this crude showed a mix-

( &)-I and ( kj-2 in 1:4

Powdered

of (?)-z

H20. The

were dried with anh

~R)-5-rac?thylOxOl~-2-one,

optically

with

at reduced pressure to give 206 mg of a crude.

of 2 (28 % yield). The spectrosco-

pic data

10 min, then

for

washed

ting material l_, 194 mg of ( ?)-I! (32 % yield) mg

of

in 18 ml of anh DME a

and

174

PhSH

With

amount of NaPhS was added. The mixture

allowed

with

throilgh silica

4,

and ice-cooled solution

1.3 mmol)

(125 mg,

combined

at reduced

of protoanemnnin,

stirred

solution of PhSH (143 mg, 1.3 mmol) and a cata-

and

mg of a residue,

of

a

CHC13

dried

removed

chromatography

as eluent,

with

liquors

solvents

to give

column

(m,

to

123 flOO1, 115 (12.51, 110 (241, 109

(12.5).

of

to stand at 02 for 10 min, then

layer

Na2S0,.

g

( tj-9

3.06

1790.

(21, 207

1.5). 218 134

9:l

(CDC131,

1170, 1030 and 995 cm-1; MS, m/e

_S.

with CHC13 and washed with water. The

aqueous

of

from

0.64 g of it)-.

1H); 3.19 (d, J=5.3; 2H); 3.79 (m, 1H);

4.60 IR

m.p.

were

through silica

acetate

0.25

(41 %

yield),

lytic

allowed

using

hexane-ethyl

2

was

by

a crude mixture

afforded

27 ml of anh DME was added slowly. The mixture

the

g of

2:3 ratio as eluent,

was

diluted

l.PO

Column chromatography

(r)-!3-phenylthiomethyloxol-S-en-2-one,

(+)-I_and 5-phenylthiomethyloxol-4-en-2-one. To

399

7.87.

1280,

1230,

%. requires: C. 59.98; H. 8.05 c5H8a2 in a similar way, the compounds _1, ;?,

P. CAMPS

400 6, 2, g

and 14 were correlated to Is.

ef of.

crude

from

O_(R)-5-methyloxo1-3-en-2-one B-angelica la&one), The

iodo

(1-)-(R)-

g

derivative

prepared

16.

accor-

the pyrolysis

fa} 2,0,-95.89,

torr;

was

C=O.73

acetate,

was hydrogenated

using 10 $6 Pd/C (126 mg) as catalyst, in presence

and

IR

(film),

pressure of

CHCl

The

solvent

and

the

and

was

removed

residue

filtered.

at reduced

boiled with Evaporation

50 ml of

the

3 CHCl3 afforded 696 mg of crude diastereoisomeric

2,3-P_ethoxymethylene-+deoxy-

lactone,

17,

which

by

column

1H);

3025, -1

3000,

1780,

.

the

of K2C03 (1.1 g, 8 mmol), at 3.4 atm

r.t.

PMR

1X) and 7.57 (dd, J=6,

fdd, J=6, J'Q.6;

1350, 1190, 1070 and 980 cm

ethyl

.

6.17

in

of

CHCf

3H); 5.20 (d, .J=',,1H);

J'=1.3;

ml

in

to

lOOQ/14

fCDCl3f. 1.48 (d, J=6;

ding to ref. 1, (1.26 g, 4.01 mmol) dissolved 25

distilled

(226 mg, 87 % yield); b.p.

afford g

Acknowledgements.I.N.A.P.E.

Ministerio

to O.P.

is gratefully

the Comision Asesora

fellowship

A de

Educaci6n

y

acknowledged.

from Cieneia

We thank

de Investigation

Cienti-

fica y Tecnica for financial support.

y-ll_ribonoREFERENCES

chromatography

through silica gel, using a mixture of CH2CI2hexane

(1:7) as eluent, gave pure 17 (627 mg,

63 % yield]. abs,

PMR

(CDC13), 1.00-1.30

1.

(complex

Ao

3H); 1.45 (d, J=7.3; 3H): 3.25-3.70 fccm-

plex

abs,

2H);

(4.38-4.90

0.

and 5.87 fs, 1H); IR (film), 3000, 1780, 1350,

2),

177

119

(51, 117 (5), 99 (32). 97 (201, 89 (9)s

88

(lo), 145

(171, 87

(9), 83

0. Ponsati, See

also:

connected to a rotary microdistilla-

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and heated at 220*/l atm. The

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2332

2.

Amer. --

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was

2359

Sot. -

and 69 (681.

mmol)

Letters,

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(9f, 76 (131,

(587 mg, 312

38.

J. Font

1, 1 (1922).

4.

10 ml flask containing g

Camps,

Ortu-

(1981).

75 (100)‘ 73 flS), 72 (71, 71 (lOO), 70 (lOa)

A

Tetrahedron, P.

Tetrahedron

Ponsatf,

2. Y. Asahina and A.

(71, 144 (23). 143 (loo),

(23). 85

and

(1982).

(complex abs, 4H)

1190, 1060 and 980 cm-1; MS, m/e (%I 178 CM+.

P. Camps, J. Cardellach, 3. Font, R.M.

Chim. w,

5,

and R. Scheffold, Helv.

2272 (1981).

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