- Email: [email protected]
The stereospecific synthesis of D,L-Winterin
1965: Pergamon PreesLtd. Tetrahedron Letters No.49,PP,4429-4451, Printed in Great Britain.
THE STEREOSPECIFICSYNTHESIS OF D,L-WINTERIN 0ottfrled Drieger ChemistryDepartment Oakland University Rochester,Michigan
(Received 20 September
1965)
Winterin (I), Is one member of a series of closely related bicyclofarnesolderivativesfound in the bark extracts of D.wlnterin (1). A recent paper (2) illustratesone approach to the synthesisof drlmanic sesqulterpenes. We were interestedin a generallyuseful syntheticroute to these compoundsas well as to structurallyrelated diterpenes. Our approach,which introducesthe entire A ring directly, 1: Illustratedby a stereospecificsynthesisof winterin.
I.
II.
III.
The olefin, l-vinyl-2,2,6-trimethylcyclohexene (II), is readily prepared by thermal decarbo-ylationof g-cyclocltrylideneaceticacid (3).
4429
4430
NO.49
A Diels-Alderreaction with acetylenedlcarboxylic acid was effected in diglyme at 97'C for 24 hours. After removal of the solvent in vacua and cooling, the adduct III, as the anhydrlde, can be isolated directly. After recrystallization from ether, III exhibits a m.p. of 142-143'C.* The yield of nicely crystallineproduct is 4%. The Infrared spectrum of adduct III closely resembles that of winterln (4), having strong absorbtlonsat 5.45 and 5.6gb (anhydrldeC=O) and two weak bands at 5.95 and 6.18~ (C=C stretching). The n.m.r. spectrum Is also consistentwith the assigned structure,having absorbtlonsat 1.14 and 1.20 p.p.m., assigned to the C4 gem dimethyl protons; 1.47 p.p.m. (Cl0 methyl protons); a doublet at 3.06 p.p.m. (J_5cps)assigned to the allyllc methylene group at C7; and a triplet at 5.71 p.p.m. (J=5 cps) assigned to the C6 vinyl proton, (CHCl3, TMS standerd). CatalytichydrogenationIn glacial acetic acid with 10% Pd/C, followed by preparativethin-layer chromatographyon silica gel 0, gave a crystallineproduct, m.p. 153-154'C.rin 3076yield. A mixed m.p..with authentic (4) wlnterln (I) gave no depression. Its infrared, ultraviolet,and n.m.r. spectrum as well as its TLC behavior Is Identical with winterin. The only other product observed on hydrogenationwas the tetrahydroderivativeof III. The hydrogenationmust thereforehave followed a stereospecific
* Satisfactoryanalyses were obtained on all new compounds.
4431
No.49
course leading only to the trans A/B ring juncture. There Is adequate precedent for the steric outcome of catalytichydrogenation of related compounds in the literature (5).
The stereochemistry
of winterln has already been deduced by comparisonwith confertlfolin(1). We are continuingto explore this approach. Acknowledgement. We gratefullyacknowledgepermission to utilize the RMR spectrometerof Ford Research Laboratories, Dearborn, Michigan, the able technical assistance of W. M. Pelletier,and the support by the PetroleumResearch Fund of the American Chemical Society.
References (1) H. I-I. Appel, R.P.M. Bond, and K. Ii.Overton, Tetrahedron, 2,
635
(1963).
(2) E. Wenkert and D. P. Strike, J. Am. Chem:Soc., 86, 2044 (1964). (3)
E. E. Royals, J. Am. Chem. Sot., 6&
841’(1947)
(4)
Kindly donated by ProfessorK. Ii.Overton.
(5)
Q. Stork and H. Schulenberg,J. Am. Chem. Sot., z,
250 (1956);
K. Raman and P. N. Rao, Tetrahedron3, 294 (1958); D. A. H. Taylor, J. Chem. Sdc. 3319
(1961);
and J. E. Davies, J. Am. Chem. Sot. B,
3419
G. Stork, A. Melsels, (1963)
inter al.,
but for a proviso see E. Wenkert, A. Afonso, P. Beak, R. W. J. Carney, P. W. Jeffs, and J. D. McChesney, J. Org. Chem. z 713 (1965).
THE STEREOSPECIFICSYNTHESIS OF D,L-WINTERIN 0ottfrled Drieger ChemistryDepartment Oakland University Rochester,Michigan
(Received 20 September
1965)
Winterin (I), Is one member of a series of closely related bicyclofarnesolderivativesfound in the bark extracts of D.wlnterin (1). A recent paper (2) illustratesone approach to the synthesisof drlmanic sesqulterpenes. We were interestedin a generallyuseful syntheticroute to these compoundsas well as to structurallyrelated diterpenes. Our approach,which introducesthe entire A ring directly, 1: Illustratedby a stereospecificsynthesisof winterin.
I.
II.
III.
The olefin, l-vinyl-2,2,6-trimethylcyclohexene (II), is readily prepared by thermal decarbo-ylationof g-cyclocltrylideneaceticacid (3).
4429
4430
NO.49
A Diels-Alderreaction with acetylenedlcarboxylic acid was effected in diglyme at 97'C for 24 hours. After removal of the solvent in vacua and cooling, the adduct III, as the anhydrlde, can be isolated directly. After recrystallization from ether, III exhibits a m.p. of 142-143'C.* The yield of nicely crystallineproduct is 4%. The Infrared spectrum of adduct III closely resembles that of winterln (4), having strong absorbtlonsat 5.45 and 5.6gb (anhydrldeC=O) and two weak bands at 5.95 and 6.18~ (C=C stretching). The n.m.r. spectrum Is also consistentwith the assigned structure,having absorbtlonsat 1.14 and 1.20 p.p.m., assigned to the C4 gem dimethyl protons; 1.47 p.p.m. (Cl0 methyl protons); a doublet at 3.06 p.p.m. (J_5cps)assigned to the allyllc methylene group at C7; and a triplet at 5.71 p.p.m. (J=5 cps) assigned to the C6 vinyl proton, (CHCl3, TMS standerd). CatalytichydrogenationIn glacial acetic acid with 10% Pd/C, followed by preparativethin-layer chromatographyon silica gel 0, gave a crystallineproduct, m.p. 153-154'C.rin 3076yield. A mixed m.p..with authentic (4) wlnterln (I) gave no depression. Its infrared, ultraviolet,and n.m.r. spectrum as well as its TLC behavior Is Identical with winterin. The only other product observed on hydrogenationwas the tetrahydroderivativeof III. The hydrogenationmust thereforehave followed a stereospecific
* Satisfactoryanalyses were obtained on all new compounds.
4431
No.49
course leading only to the trans A/B ring juncture. There Is adequate precedent for the steric outcome of catalytichydrogenation of related compounds in the literature (5).
The stereochemistry
of winterln has already been deduced by comparisonwith confertlfolin(1). We are continuingto explore this approach. Acknowledgement. We gratefullyacknowledgepermission to utilize the RMR spectrometerof Ford Research Laboratories, Dearborn, Michigan, the able technical assistance of W. M. Pelletier,and the support by the PetroleumResearch Fund of the American Chemical Society.
References (1) H. I-I. Appel, R.P.M. Bond, and K. Ii.Overton, Tetrahedron, 2,
635
(1963).
(2) E. Wenkert and D. P. Strike, J. Am. Chem:Soc., 86, 2044 (1964). (3)
E. E. Royals, J. Am. Chem. Sot., 6&
841’(1947)
(4)
Kindly donated by ProfessorK. Ii.Overton.
(5)
Q. Stork and H. Schulenberg,J. Am. Chem. Sot., z,
250 (1956);
K. Raman and P. N. Rao, Tetrahedron3, 294 (1958); D. A. H. Taylor, J. Chem. Sdc. 3319
(1961);
and J. E. Davies, J. Am. Chem. Sot. B,
3419
G. Stork, A. Melsels, (1963)
inter al.,
but for a proviso see E. Wenkert, A. Afonso, P. Beak, R. W. J. Carney, P. W. Jeffs, and J. D. McChesney, J. Org. Chem. z 713 (1965).