Photocycloaddition of Enynones (4-Acylbut-1-en-3-ynes) to Alkenes

Abstract

The title compounds undergo regio- and diastereoselective [2+2]-cycloaddition at the olefinic C-C bond on irradiation (350 nm) in the presence of either methacrylonitrile or 2,3-dimethylbuta-1,3-diene, affording hitherto unknown 1-cyclobutylalk-1-yn-3-ones or 1-bicyclo[4.2.0]octylalk-1-yn-3-ones, respectively.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“… 442 − 444 A remarkable intermolecular [2 + 2] photocycloaddition of enynones to olefins was reported by Inhülsen and Margaretha. 445 Reactions occurred at the terminal olefin position to form HH type products as shown for the reaction 241 → rac - 242 ( Scheme 76 ).…”

“…There are rare cases in which intramolecular[2 + 2] photocycloaddition reactions were successfully performed with open-chain α,β-unsaturated aldehydes and ketones. The reactions typically include the formation of a bicyclo[3.2.0]heptane skeleton with the first step being a fast five-membered ring closure, which successfully competes with cis/trans isomerization.442−444 A remarkable intermolecular[2 + 2] photocycloaddition of enynones to olefins was reported by Inhulsen and Margaretha 445. Reactions occurred at the terminal olefin position to form HH type products as shown for the reaction 241 → rac-242 (Scheme 76).…”

Chemo- and Regioselective Synthesis of Alkynyl Cyclobutanes by Visible Light Photocatalysis

“…7 Only a few terminal and cyclic enynone gave [2 + 2] adducts as the sole products with moderate efficiency (Scheme 1b). 8 During the past few years, successful visible-light-induced photocycloadditions of aryl olefins, enones, and 1,3-dienes have been reported. In several of these studies, it was shown that triplet sensitization is a successful way to facilitate the reaction, even in an enantioselective fashion.…”

Intramolecular Pyridone/Enyne Photocycloaddition: Partitioning of the [4 + 4] and [2 + 2] Pathways

“…We recently reported the first [4 + 4] cycloadditions of enynes, performed by irradiation of an enyne/2-pyridone mixture, Scheme . − This reaction of commercially available reagents yields a rich mixture of products, derived from a competition between [2 + 2] and [4 + 4] pathways, both of which produce an array of regio- and stereochemical isomers. Of the six potential constitutional isomers 3 − 8 , examples of all but 8 were isolated.…”