Intermolecular 2+2 imine-olefin photocycloadditions enabled by Cu(I)-alkene MLCT

2 + 2 Photocycloadditions are idealized, convergent construction approaches of 4-membered heterocyclic rings, including azetidines. However, methods of direct excitation are limited by the unfavorable photophysical properties of imines and electronically unbiased alkenes. Here, we report copper-catalyzed photocycloadditions of non-conjugated imines and alkenes to produce a variety of substituted azetidines. Design principles allow this base metal-catalyzed method to achieve 2 + 2 imine-olefin photocycloaddition via selective alkene activation through a coordination-MLCT pathway supported by combined experimental and computational mechanistic studies.

An ideal method to construct azetidines would be through a [2 + 2] photocycloaddition that joins an olefin and an imine, shown only rarely in the literature, partially due to competitive photochemical processes of the imine. Here, the authors report copper-catalyzed photocycloadditions of imines and alkenes to produce a variety of substituted azetidines, via activation of the olefin.

Donor–acceptor fluorophores as efficient energy transfer photocatalysts for [2 + 2] photodimerization

Donor–acceptor fluorophores can act as efficient energy transfer photocatalysts to activate enone substrates, realizing photodimerization and isomerization reaction of enone substrates without precious metal photocatalysts.

Stereocontrolled Preparation of Diversely Trifunctionalized Cyclobutanes

The expedient and stereoselective syntheses of small libraries of trifunctionalized cyclobutane scaffolds bearing an acid, an amine, and a third functional group are described. Starting from a single precursor, the readily available protected derivative of all-cis-2-amino-3-hydroxycyclobutane-1-carboxylic acid, cis-trans stereoisomers are obtained following an S_N2-type reaction, while all-trans stereoisomers are obtained using the same strategy preceded by a C1 epimerization reaction.

Development of an Alkyne Analogue of the de Mayo Reaction: Synthesis of Medium-Sized Carbacycles and Cyclohepta[b]indoles

Embedded medium-sized carbacycles and cyclohepta[b]indoles occur frequently as scaffold elements in natural products and bioactive compounds. Described herein is a conceptionally novel photochemically triggered cascade process to these scaffolds. Key to the cascading ring-expansion process is an unprecedented intramolecular alkyne analogue of the de Mayo reaction.

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

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4 , whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.