A total synthesis of (+)-taxusin (1) has been realized by virtue of the development of a practical route for complete functionalization of the A ring. To achieve this goal, it proved necessary to devise a strategy that would enable chemical transformations to proceed in a very congested environment. The successful pathway from 2 required 19 steps consisting principally of chemoselective oxidation and reduction maneuvers of various types. The requisite methyl substituent was introduced by 1,2-addition of the methylcerate reagent to a C(12) ketone intermediate. Several tactics that ultimately proved unsatisfactory are also discussed in an effort to set important boundary limits on chemical reactivity. The pivotal roles played by samarium diiodide and tetrapropylammonium perruthenate in permitting the deployment of appropriate chemical changes are noteworthy.

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Abstract

Dedicated to Albert Eschenmoser on the occasion of his 70th birthday ( 2 8 . N . 95) A new general concept for the total synthesis of pseurotin A (l), a secondary metabolite of Pseudeurotium ovalis STOLK, which possesses a highly substituted 1 -oxa-7-azaspiro[4.4]nonane skeleton, is presented. A key intermediate of the planned reaction sequence is the functionalized y-lactone 8. The corresponding protected compound 52 was prepared using (S)-0,O-isopropylideneglyceraldehyde (13) and the bromoacetall4 as starting material. y-Lactone 52 was obtained in enantiomerically pure state in ten steps. It possesses the desired configuration.

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