Russian Chemical Bulletin, International Edition, Vol. 55, No. 4, pp. 703—707, April, 2006 703 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 678—682, April, 2006. 10665285/06/55040703 © 2006 Springer Science+Business Media, Inc. Photooxidative dehydrogenation of ∆ 8 drimen and ∆ 8 11homodrimen7ones into α,α´ dienones P. F. Vlad, a M. N. Coltsa, a A. N. Aricu, a A. G. Ciocarlan, a E. C. Gorincioi, a C. G. Edu, a and C. Deleanu b a Institute of Chemistry, Academy of Sciences of the Republic of Moldova, 3 ul. Academiei, MD 2028, Chisinau, Republic of Moldova*. Fax: +7 (373 2) 73 9775. Email: vlad_p@mail.md b Institute of Organic Chemistry of the Romanian Academy of Sciences, ul. Independentei, 202B, RO71141 Bucharest, Romania.** Fax: (401) 627 6366. Email: calind@fx.ro An efficient twostep procedure for photooxidative dehydrogenation of drimane and 11homodrimane compounds containing an 8en7one structural unit into α,α´dienones was elaborated. The method is based on the transformation of ketones into the respective enol acetates followed by photosensitized oxygenation. Methyl 7oxo11homodrima5,8dien 12oate, 5,6dehydro7ketoisodrimenine, 11acetoxydrima5,8dien7one and 11,12di acetoxydrima5,8dien7one were prepared in high yields starting from methyl 7oxo11 homodrim8en12oate, 7oxoisodrimenine, 11hydroxydrim8en7one and 11,12di acetoxydrim8en7one, respectively. Key words: photosensitized oxygenation, photooxidative dehydrogenation, drim8en7 ones, drima5,8dien7ones, methyl 7oxo11homodrim8en12oate, methyl 7oxo11 homodrim5,8dien12oate. Aimed at preparing 11homodrimane derivatives with oxygencontaining functional groups at the С(6) and C(9) atoms from readily available methyl 7oxo11homodrim 8en12oate (1), 1 we studied the photooxidative oxy genation of the enol acetate derived from 1, namely, me thyl 7acetoxy11homodrimа6,8dien12oate (2), in the presence of tetraphenylporphyrin (H 2 tрр). We took into account the fact that conjugated 1,3dienes preferably react with singlet oxygen according to the [4+2]cyclo addition pattern to give endoperoxides. 2,3 However, data from elemental and spectral analyses convincingly dem onstrated that the reaction product formed in high yield (93%) was not endoperoxide (3). The molecule contained no peroxide or acetate groups, but the ester function re tained and a dienone group appeared (IR and 1 H and 13 C NMR data). Hence, the product was identified as methyl 7oxo11homodrimа5,8dien12oate (4) (Scheme 1). Previously, we have synthesized this com pound 1 by dehydrogenation of oxo ester 1 with selenium dioxide. The physicochemical and spectral characteristics of compound 4 prepared from oxo ester 1 by these two methods were fully identical. It is noteworthy that photo sensitized oxygenation of enol ester 2 is a more efficient and convenient route to dienоne ester 4, because the reaction of oxo ester 1 with SeO 2 gave not only the target product 4, but also organoselenium byproducts that are difficult to separate. It was of interest to elucidate whether the twostep transformation of oxo ester 1 into dienone ester 4 that we found is common to enones of the transdecalin series with similar structures, in particular, drimane compounds. Therefore, we used this approach to prepare natural oxo lactone 7 isolated from the moss Porella cordeana. 4 7Oxoisodrimenine (5) served as the starting compound. 5 Enol acetate 6 was photooxidized with oxygen in the pres ence of H 2 tрр to give the target compound 7 in high yield (69%). When Bengal Rose was used as the photo sensitizer instead of H 2 tрр, the yield of the reaction prod uct decreased to 57%. This synthesis has been described previously. 6 Then we investigated photooxidative dehydrogenation of 11hydroxydrim8en7one (8). 7 Its reaction with isopropenyl acetate in the presence of TsOH did not pro ceed to completion even on longterm refluxing and af forded a complex mixture of compounds in which the desired 7,11diacetoxydrimа6,8diene (9) was the major component. Its structure was confirmed by data from el emental and spectral analyses data. A twostep route to diacetoxy diene 9 from hydroxy ketone 8 proved to be more efficient and convenient. Compound 8 was ace * Institutul de Chimie al Academiei de tiin e a Moldovei, str. Academiei 3, MD 2028, Chi inãu, Republica Moldova. ** Institutul de Chimie Organic al Academiei Române, Spl. Independentei 202B, Bucure ti, România.