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Investigations of alpha-siloxy-epoxide ring expansions forming 1-azaspirocyclic ketones

TitleInvestigations of alpha-siloxy-epoxide ring expansions forming 1-azaspirocyclic ketones
Publication TypeJournal Article
Year of Publication2004
AuthorsDake, GR, Fenster, MDB, Fleury, M, Patrick, BO
JournalJournal of Organic Chemistry
Volume69
Pagination5676-5683
Date PublishedAug
Type of ArticleArticle
ISBN Number0022-3263
Keywords1ST TOTAL-SYNTHESIS, ALDOL ALDOL PROCESS, ASYMMETRIC-SYNTHESIS, BAEYER-VILLIGER OXIDATION, LEWIS-ACIDS, ORGANIC-SYNTHESIS, PRACTICAL, QUATERNARY CARBON CENTERS, REARRANGEMENT, SEMI-PINACOL, SILYL ETHER REARRANGEMENTS, STEREOSELECTIVE CONSTRUCTION
Abstract

The construction of 1-azaspirocyclic cycloalkanones using a siloxy-epoxide semipinacol ring expansion process was examined. Functionalized 1-azaspiro[5.5]undecan-7-ones (1-azaspirocyclic cyclohexanones) proceeded in high chemical yields with complete diastereoselectivity using titanium tetrachloride as the Lewis acid promoter. The formation of functionalized 6-azaspiro[5.4]-decan-1-ones (1-azaspirocyclic cyclopentanones) proceeded in high chemical yield with little diastereoselectivity. Modification of reaction parameters such as the Lewis acid promoter or the nature of the silyl ether allowed for the preferential formation of either ("anti" or "syn" 1,2 alkyl shift) diastereomeric product. An explanation for the different reactivity profiles between the cyclobutanol silyl ethers and cyclopentanol silyl ethers is provided.

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