Revised conformational assignments in 1,3-dimethyltrimethylene sulfites

TetrahedronLettersNo.14, PP_ 1109-1112,1969. PergemonPress. Printed in Great Britain.

REVISED CONFORMATIONAL

ASSIGNMENTS

IN 1,3-DIMETHYLTRIMETHYLENE

SULFITES

Gordon Wood and M. H. Miskow Department

of Chemistry, Windsor,

(Receivedin USA 27 January 1969; Although

the conformation

the conformational

We have measured and the results assignments

publication

properties

the dipole moments

sulfite and related compounds (l), further work is required

of this interesting

Our data and the corresponding

(4).

are presented

Table

Dipole moments

in Table

system

of the three 1,x-dimethyl

indicate the need for revision of the original

compounds

I.

of Windsor

receivedin UK for publication19 February1969)

of trimethylene

has been the subject of extensive to establish

University

Ontario, Canada

numbers

II

compounds

conformational

for the 2-t-butyl

I.

(20°)a Solvent

Compound

2-t-butyl-trimethylene

(2).

sulfite

1,

f1

1,3-dimethyl-trimethylene

cc1 4

C6H6

(I)

3 .61b

3 .66b

(11)

3 .76b

4.00b

(A) (meso)

3.51

3.60

5.31

5.37

3.93

3-93

sulfite

11

II

I,

(B)

1,

II

I,

CC) Cdl)

a. Calculated according to ref 5. agree with ref la within 0.1 D.

b.

beso)

Ref la.

1109

Our determinations

generally

1110

No. 1’1

van Woerden

(la) has made extensive use of dipole moments

and in particular,

the moments

carbon tetrachloride

of the 2-t-butyl

Isomer II was considered

chair forms, with the more polar S=O equatorial

forms to be in equilibrium

sider isomer IT as a non-chair that low temperature

form favored in polar solvents.

identical with room temperature

and we, therefore,

(to -9g" =n acetone-d spectra

chair conformation

is axial and both methyl groups are equatorial. to isomer A of this set, since its moments of the 2-t-butyl

6

)of isomer11 are

series can take up the in which the S=O group

We assign this conformation

correspond

to those of isomer I

pair.

Isomer B has a moment which is unusually solvents used.

prefer to con-

(6).

One of the two meso isomers in the 1,3-dimethyl (for these compounds)

is too high

In agreement with this view is the fact

form.

nmr spectra

with

to be a mixture of

the barrier to ring flipping in these compounds

In our opinion,

preferred

in benzene and in

allowed isomer I to be assigned a chair conformation

S=O axial and t-butyl equatorial.

for the chair

compounds

in his analysis,

large and constant

Its nmr spectrum and behavior

on acid treatment

little doubt that it is the other meso isomer. consistent

with the chair conformation

therefore,

assign this orientation

in the (~0 leave

The size of the moment is

with equatorial

S=O (e), and we,

to the S=O group and locate the methyl

groups equatorially. Isomer C (racemic) may be either a distorted Recent nmr and ir evidence a mixture

about 30% non-chair

sulfites

(9) suggests

for isomer C.

This leaves

as to why the moment does not change with solvent nor the nmr

spectrum with temperature. hexanes,

from a series of racemic

of forms including

the question

chair or a flexible form.

It may be that for some sulfites, unlike cyclo-

certain arrangements

This idea corresponds

within the flexible form are strongly preferred.

to our general view that torsional

barriers

No014

1111

(6),

in the sulfites are high

so that we are not inclined to admit the presence

of any chair form for isomer C until some specific evidence In summary, we believe 1,3_dimethyltrimethylene

the correct conformational

isomer B

It should be emphasized

chair conformation

the axial 1,x-dimethyls

for the

isomer C

that isomer B is the first cyclic

exist in a chair form with S=O equatorial would

sulfite to

and that in this compound the

suffer very serious interactions

from

and axial S=O group.

The authors wish to thank the Department and the National

assignments

sulfites are as follows:

isomer A

alternative

for it is found.

of University

Research Council of Canada for financial

work and the latter for Scholarships

to M.H.M.

Affairs of Ontario supportof this

(1966-69).

REFERENCES 1.

(a) 341,

2.

H. F. van Woerden

and E. Havinga, Rec. Trav. Chim. Pavs-Bas, &,

353

references

(1967);

(b)

Electron diffraction

patterns

contained therein.

of the three 1,x-dimethyl

isomers are now

being analyzed by Prof. J. L. Hencher of this department. study on trimethylene

sulfite has been reported

3.

C. Altona, H. J. Giese and C. Romers, -', ibid

4.

P. c. Lauterbur,

5307

(1963).

la, P 353),

J. G. Pritchard,

our conclusions

85, 1197

and R. L. Vollmer,

When the S=O assignments

An X-ray

(3). (1966). J. Chem. Sot.,

in this work are reversed

for isomer A agree.

(ref

In our opinion, the nmr

and ir evidence presented by these authors for the other isomers is far from conclusive.

5.

F. Mall and E. Lippert,

Z. Electrochem.,

58,

853

(1954).

1112

6.

No, 14

(a)

Other recent work on molecules

high rotational

barriers;

J. Kenney, Jr., Tetrahedron

letters,

S. Dewar, and W. R. Jackson,

(b)

5055 (1968); A. H. Cowley, M. J.

J. Am. Chem. Sot., 90, 418" (1968);

See also A. Rauk, S. Wolfe,

3.7-j113 (1969). Calculations related molecules

with vicinal electron pairs indicates

e.g., M. Raban, F. B. Jones, Jr., and G. W.

and I. G. Csizmadia,

on hydrogen

methyl

not only relate high rotational

Can. J. Chem.,

sulfinyl anion and barriers

to inter-

action of vicinal electron pairs, but further suggest that the favored conformation

in such molecules

conformation

of cyclic sulfites.

7.

Addition

8.

Calculations conformation. P. Maroni

to the S=O axial

of a trace of acid converts this compound cleanly

corresponding

9.

(p. 128) corresponds

isomer A. (ref la) would suggest a moment of 5.0-5.2 D for this Private communication

and L. Cazaux, Abstracts

the Chemical

into the

Institute

from H. F. van Woerden.

of the 5lst Annual Conference

of Canada, Vancouver,

June, 1968.

of