3-Lithio-y-pyrone

Intermediate 40 would be produced through a coupling reaction between the appropriately functionalized decalin aldehyde 41 (available from alcohol 42) and 3-lithio-y-pyrone 23. Intermediate 42 would be formed through the strategic [2,3]-Wittig rearrangement of stannylmethyl ether 43. On the basis of the results accumulated from the nalanthalide synthesis (cf. Section Total Synthesis of (—)-Nalanthalide and Scheme 6), we expected that the C9 stereogenic center and the C8 exo-methylene function in the product 42 would be simultaneously formed. Intermediate 43, in turn, would be derived from 14 [17]. 

A-C, intermediate 90 was expected to be synthesized by a coupling reaction of the appropriately substituted decalin aldehyde 91 with 3-lithio-y-pyrone 23. Intermediate 91 would be prepared from the common intermediate 29 available from 15 (cf. Scheme 5). 

Dihydro-y-pyrones and dihydro-3-furanones.1 A new synthesis, of dihydro-y-pyrones (5) and dihydro-3-furanones (8) involves conversion of (1) into 2-lithio-2-(2 >2 -dimethoxyethyl)-l,3-dithianc (2) by treatment with n-butyllithium in THF at -30°. Treatment of (2) with an epoxide gives (3). On treatment with p-toluenesulfonic... 

Lithio-2-(2,2-dimethoxyethyl)-l,3 dithian, when it reacted with ketcmes and epoxides, led to intermediates which were converted in somewhat low yield into 3-furanones and dihydro-y-pyrones, respectively. " 2-Methyl-2-lithio-dithian reacted efficiently with spiro-epoxide groups at positions 3 and 17 in steroids. The products obtained in this manner were further elaborated for example, 3a-ethyl-30-hydroxy-5a-cholestane, " 3-acetonyl-A -androstane, and both isomers of 17-acetonyltestosterone " were prepared. The carbon skeleton, including the S-lactone ring, of pestalotin... 

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