Epoxide opening cuprate mediated

The bromo epoxide 402 used in these syntheses is prepared from 371 by initial conversion to (iS)-l,4-dibromo-2-butanol (401) [16] followed by cyclization with potassium hydroxide [18]. Alkylation of 1,3-dithiane first with EE-protected co-chloroalcohols to give 403 and then with the ( S)-epoxide 402 affords 404. Opening the oxirane with either Super-Hydride or methyl cuprate creates the requisite carbon skeletons 405 with the appropriate fimctionality patterns. Removal of the EE protecting group and mercury-mediated hydrolysis of the thioacetal directly furnishes the spiroacetals 407 as a 3 2 mixture of diastereomers [16]. 

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