Chiral acylsilanes synthesis

Startg. chiral acylsilane treated with 2 eqs. -BuLi in THF at —78° for 5 min intermediate hydroxysilane (Y 92% diastereomer ratio > 100 1), treated with BU4NF in DMF at room temp. 5yn-product. Overall Y 89% (diastereomer ratio > 100 1). The diastereomer ratio is noticeably lower (5 1) by direct reaction from the corresponding aldehyde. F.e. inch reaction with allyltrimethylsilane (in the presence of TiCy and with allylmagnesium bromide s. M. Nakada et al., J. Am. Chem. Soc. 110, 4826-7 (1988) review of synthesis and synthetic potential of acylsilanes s. A. Ricci, A. DeglTnnocenti, Synthesis 1989, 647-60 review of the steric influence of the trimethylsilyl group s. J.R. Hwu, N. Wang, Chem. Rev. 89, 1599-615 (1989). 

Two alternative routes to (+)-swainsonine (ent-37S) developed by Chen and Tsai, Hke that used in their synthesis of lentiginosine (c Scheme 47 Section 3.3.2), created the bond to C-8a by means of free radical cycUzations onto an acylsilane. The first approach entailed the creation of the C-l/C-8a bond (Scheme 86). Amide formation between the amine 638 and the acid chloride prepared in situ from the chiral lactone-acid 639 yielded (—)-640, which was cyclized with base to the imide (—)-641 in 91% yield. Chemoselective reduction of the C-2 carbonyl group, acid-catalyzed reaction with thiophenol, and protection of the hydroxyl substituent as the benzoate gave 642 as a mixture of isomers. After hydrolysis of the dithiane to the acylsilane 643 with iodobenzene bis(trifluoroacetate), treatment with tri-butyltin hydride and l,lCazobis(cyclohexane-l-carbonitrile) (ACCN) as radical initiator produced the indohzidin-5-one 644 in 86% yield as a... 

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