Tetrahedron Letters No. 43, pp.3985 - 3986, 1971. Pergmon Preaa. Printed in Great Britain.

THE PREFERRED COIyF0H4M'IOg OF BICYCLO~,3,2]DECMiE

By Martin Daylel, Rweell Hafter' aud William Parker*

Department of Chemistry, Univereity of Btirling, Stirling, Bcotland.

(Received in IE 1 September 1971; accepted for publication 22 September 1971)

The preferred conformationa (1) and (2) have been aeeigmd2 to bicyclo[3,3,2]

decant-g,iO-semi&one and bicyclo[3,2,~]nonan-6,7-semidione, on the basis of e.6.r. hyperfine

splitting con&ante. Extrapolation of thie data led to the pro~oeal that bicyclob,3.2]

decane itself preferred the be&-chair3 conformation (3(b)). %mmr. the tr8Mposition

of the conformational preferences of flaxible molecular ee(pncnts frCm ring BYstem to

ring system without consideration of the molecule in question (LB a whole can often lead

to erroneous conclueione.

0' Q’

(1) (2)

The solution infra-red rpectra of certain bicyclo(3,3,2)decana derivativee exhibit

the high frequency v(CH) aad 6(CH) abrorption bande umally aesociated with interaction

between two or< more methylene group8 in close proxi.mityb. Such abnormally high

absorption bande muat be areociated with traneanuular metbylene interact&me between

C-3,c'T in conformation (3a), or between C-3, C-9(or C-10) in conform&one (3b) and (3~);

or between C-2, c-6 (or C-4, C-8) in conformation 3(d).

38 3b 3c

We have now investigated the 6(CH) bands of a number of such compounds.

3985

3d

3986 No. 43

Bioyclo(3,3,2)decane and the correspondi= 9-alcohol, g-acetate5 and P-ketone exhibit

bands at 1484; 2982 and 1483, 1486; aud 1470 cn~-' respectively whereas no such abnormal

absorptions are detectable for the 2-olefin5, 3-ketone5'6 or 2-ene-g5 md 2-ene-lo-ketone5.

Further, the 9 ,lO-diketone5, and evermore &nificantly, 9-oxabicyolo[3,3,3]decane-lG-one7

shov maxima at 1485; 2994 aud 1489 cat-', thus euuuortiug the viev that these high frequency

bands arise from methy1ene-methylene interactions between C-3 and C-7 in the tvin-chair --- --

conformation (3a) or between C-2 and c-6(o_r C-4 and (c-8) in the twin twist-boat conf~nner (3d ---.c --e---e- ---

In this context2 it is notable that the I)_olefin exhibits no abnormal 6(C-H) absorption,

though the&+rimetQQsilylether of biqclo[3,3,2]dec-9-enc9,10-dio15 show _fms at

2990 and 1489 cm-'. !Bhus, the boat-chair couformation (3b) seems to be preferred only in

those bicyclo[3,3,2]decane derivatives which are forced to adopt a fully eclipsed arrcurgement

about C-9 and C-10 (viz. the semidione and 9-olefin) (unless there are other steric factors

mitigating against this coniorraation,rrsinthcbie-tr~~~ilylcthadcecribab),wflarcM -

these compouuds which can adopt a C-9; C-10 staggered arraugcment seem to prefer a twin-chair

(or twin twist-boat) couformation. In support of this statement, it is worth noting that

the ultra-violet spectruu of bicyclo(3,3,2)-9,10-dione has A_(BtOH) 42l rm. which according

to Leonard and hader' indicate8 a small but definite etegger betveen C-9 and C-10.

REFERENCES

1. Supported by a Science Besearch Council Studentship.

2. G.A. Flussell aud R.G. Keeke, J. Amer. m. &., s, 4460 (1970). -_

3. c.f. M.P. Doyle and W. Parker, Chem. Corn,,, 319 (1969).

4. M. Stall, B. Willhala and 0. Buchi, m. m. &&., 2, 1573 (1955)

G. Chiurdoglu,!Ch.Doehaerd and B. Tursch, &?&&w. Chim.France. &, 1322 (1960).

L. de Vries and P.R. Byaeon, J. a. m., 26. 621 (1961).

D. Kivelson, S. Winstein, P. Eruck and R.L. Hansen, &. m. Chera.So~., Q. 2938 (1961).

G. ESlinton, J. Martin and W. Parker, J. m. &., I-243 (1965).

5. Satisfactory elemental analyses and spectral data have been obtained for all new Canpounde

described herein.

6. M.P. Doyle and W. Parker, Tetrehedronw., 12. 945 (1970).

7. A.C. Cope and D.M. Gale, J. Amer. chew &g., &, 3743 (1963).

8. B.J. Leonard and P.M. Madcr. J. Amer. them. @g.. a, 5388 (1950).