Ethers epoxy silyl

Rearrangement of epoxy silyl ethers. When treated with 1 equiv. of TiCl4, a-silyloxy epoxides rearrange to p-hydroxy carbonyl compounds. 

Table II. MABR-Catalyzed Rearrangement of Chiral Epoxy Silyl Ethers... 

Epoxy Silyl Ether MABR P-Siloxy Aldehyde Yield (%)... 

The sesquiterpene skeleton has also been assembled by the intramolecular nitrile oxide cycloaddition sequence. Oxime 238 (obtained from epoxy silyl ether 237), on treatment with sodium hypochlorite gave isoxazoline 239, which was sequentially hydrolyzed and then subjected to the reductive hydrolysis conditions-cyclization sequence to give the furan derivative 240 (330) (Scheme 6.93). In three additional steps, compound 240 was converted to 241. This structure contains the C11-C21 segment of the furanoterpene ent-242, that could be obtained after several more steps (330). 

Acylation of hydroxylamine with 8-2 Rearrangement of epoxy silyl ethers... 

The exceptional bulkiness of 2,6-di-tert-butyl-4-broniophenoxy ligands in MABR is essential here for the smooth rearrangement of epoxy silyl ethers, and the less bulky methylaluminum bis(4-bromo-2,6-diisopropylphenoxide) (MAIP) was found to be totally ineffective in the rearrangement of the tert-butyldimethylsilyl ether of epoxy-geraniol (139). BF3-OEt2 as an ordinary Lewis acid gave fluorohydrin 140 as sole isol-able product (Sch. 114). 

Sigmatropic rearrangement 1.12.42 Epoxy silyl ether rearrangement 1.1.2.43 Criegee rearrangement... 

The Lewis acid mediated rearrangement of epoxy silyl ether (69) affords the corresponding P-hydroxycarbonyl compound (70 Scheme 26). ... 

A pinacol-type rearrangement of epoxy silyl ethers has been used to prepare 0-hydroxy ketones, the migratory aptitudes observed... 

SUylated aldol adducts can be reached by using a nonaldol rearrangement promoted by treatment of bulky epoxy bis-silyl ethers with TMSOTf/i-Pr2NEt in methylene chloride at —50 °C (eq 95).Bulky mesylated epoxy silyl ethers also undergo this transformation however, a silyl triflate-promoted Payne rearrangement was observed as a side reaction depending on the stere ochemistry of the starting epoxide. 

The non-aldol aldol reaction of the isomeric epoxy silyl ethers has been reported to be controlled by the conformation of the transition states leading to an internal hydride shift. One isomer rearranges to the /1-silyloxy ketone whereas the other isomer gives a /I-elimination product. Substrates with substituents that favour formation of the chairlike transition state rearrange normally while those that do not undergo elimination (Scheme 59). 

A novel silyl triflate-promoted Payne rearrangement of silyloxy epoxides was reported by Jung et al When the ethyl substituted epoxy silyl ether 13 was treated with silyl triflate in the presence of a base, a mixture of four ketones, 16a-d and four aldehydes 17a-d were obtained. It has been assumed that two ketones and two aldehydes could be formed via a non-aldol process and an epoxide rearrangement, whereas the other four products through 14 and 15, a silyl triflate promoted Payne rearrangement. 

FIGURE 18.1. Stracture of tertiary carbocations with ring tension. The rearrangement of epoxy silyl ethers can be per-... 

Maruoka K, Ooi T, Yamamoto H. Organoaluminum-promoted rearrangement of epoxy silyl ethers to p-siloxy aldehydes. J. Am. Chem. Soc. 1989 111 6431-6432. 

Tanaka et al. 231) prepared (518a) from allylic alcohol (514) via the epoxy silyl ether (515), which was ring opened with diethylaluminum 2,2,6,6-tetramethylpiperidide to afford the 3-ene-l,2-diol (516) Scheme 90). 

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