Functionalized five-membered rings from acyclic unsaturated β-ketoester systems

Abstract

In Lewis acid-promoted cyclizations, both the ketoester (1) and its enol acetate (4) generate the cyclopentane (2), while the ketoester (5) under similar conditions does not form the carbobicycle (6) but is converted into the heterocycle ( 7 ) , via the monocyclic ketoester (8).

Mastering .beta.-Keto Esters

“…The same idea has been then applied both by Weiler and Sum161 to the synthesis of Latia Luciferin and by Corey et al162 to the synthesis of aphidicolin using mercuric trifluoroacetate as the Lewis acid. The process works well for the formation of cyclohexanone derivatives but fails in the case of a cyclopentanone derivative, as demonstrated by Van Tamelen et al 163 (Scheme 94).…”

Functionalized cyclopentanes via Sc(III)-catalyzed intramolecular enolate alkylation

“…5,7,8 For example, homo-prenylated β-ketoester 4 was shown to undergo intramolecular cyclization to methyl ketone 5 upon reaction with stoichiometric amount of SnCl 4 (Figure 1B.). 9 This cyclization strategy is proposed to rely on initial enolate O -stannylation with concomitant formation of equimolar amounts of Brønsted acid. An intermediate carbocation is generated upon protonation of the alkene under acidic conditions which subsequently undergoes the final enolate alkylation to result in 5 as the α- tert -alkylation product.…”

“…An intermediate carbocation is generated upon protonation of the alkene under acidic conditions which subsequently undergoes the final enolate alkylation to result in 5 as the α- tert -alkylation product. 9…”