Photochemical [2 + 2] Cycloaddition of Acetylene to Chiral 2(5H)-Furanones

Abstract

The [2 + 2] photocycloaddition of acetylene to chiral 2(5H)-furanones was investigated. The influence on the chemical yield and facial diastereoselectivity of the substituent at the stereogenic center and also the effect of a 4-methyl group were evaluated. A mechanistic proposal based on a simple theoretical conformational analysis is presented. Using a C(2)-symmetric bis(lactone) as the substrate, a diastereomeric excess higher than 98% was found.

A Study on the Photoreaction of 2(5H)‐Furanones with Substituted Acetylenes: Evidence for a Mechanistic Reformulation

“…[10] In contrast, the photoreactions of the same furanones with acety-lene wereconsiderably less effective both in terms of yield and diastereoselectivity( Scheme 2), providing complex crude products, wherein we identified several byproducts derivedf rom the photoreduction and/or electrocyclic ring opening of the primary cycloadducts. [11] These observations were consistent with previous resultsd escribed for the photoactivatedc ycloaddition of alkynes to enones. [12] In our laboratories, these difficulties werep artially solvedb ya pplying at wo-step protocol, by which 1,2-dichloroethylene was used as an acetylene surrogate in the photo-process andthen the chlorine was reductively eliminated.…”

“…During these studies, we were able to find conditions to achieve yields and facial selectivities good enough for applying some of these cycloadditions as key steps in the synthesis of diverse compounds with verified or potential biological activity . In contrast, the photoreactions of the same furanones with acetylene were considerably less effective both in terms of yield and diastereoselectivity (Scheme ), providing complex crude products, wherein we identified several byproducts derived from the photoreduction and/or electrocyclic ring opening of the primary cycloadducts . These observations were consistent with previous results described for the photoactivated cycloaddition of alkynes to enones .…”

Regioselective Formation of Silylated Cyclobutenes by the Photochemical [2+2] Cycloaddition of 2(5H)‐Furanones to Trialkylsilylacetylenes

“…[8] The butenolide photochemical cycloaddition has been extended to use ethyne as a reaction partner to afford cyclobutenes in modest yields. [9] As regards the stereochemistry of such [2+2] cycloadditions, reasons for such regioselectivity are discussed. The anti/syn stereoselectivity of the photocycloaddition depends on the nature of the alkyl group on the silicon atom in the starting silylacetylenes.…”

(S)-γ-Hydroxymethyl-α,β-butenolide, a Valuable Chiral Synthon: Syntheses, Reactivity, and Applications

“…The same group has extended its investigation using acetylene. 75,76 Yield and selectivity were quite similar to those obtained with ethylene (Table 5), even with methoxycarbonyl or benzoyl moieties where different steric hindrances They have also investigated the impact of a substituent on the double bond in [2+2]…”