Three‐Component Gallium(III)‐Promoted Addition of Halide Anions and Acetylenes to Donor–Acceptor Cyclopropanes

Abstract

A new strategy for the three-component addition of halide anions and acetylenes to donor-acceptor cyclopropanes (DACs) is presented. This reaction, which occurs with high E selectivity, is promoted by gallium(III) salts and based on the 1,2-zwitterionic reactivity of DACs. It opens up a new group of processes involving DACs. The reaction occurs readily with a broad range of substrates and is tolerant of various functional groups. This methodology makes it possible to assemble highly functionalized vinyl halides, which are very convenient building blocks in organic synthesis. A possible mechanism of this reaction and its stereochemical aspects are discussed in detail.

Four‐Membered Cycle Formation Challenge: GaCl3‐Promoted Formal [2+2]‐Cycloaddition of Donor–Acceptor Cyclopropanes to Bicyclobutylidene

“…The formation of propellanes 4 is very sensitive to reaction conditions and requires individual optimization for each substituted DAC 1 . It primarily concerns the precise control of the temperature[16a], of the second process stage: Table demonstrates the wide range of optimum temperatures for apparently rather similar substituents.…”

“…The mechanism of formation of [3.3.2]‐propellanes 4 appears to be rather obvious, based on the preliminary generation of 1,2‐zwitterions 2 upon treatment of DAC 1 with GaCl 3 (Scheme ) , . Subsequently, the carbocationic center attacks the double bond in bicyclobutylidene.…”

“…An extensive group of processes that should be distinguished separately occur via in situ generation of 1,2‐zwitterionic gallium complexes ( 2 ) in the presence of Ga(III) compounds (Scheme ). The [4+2]‐annulation involving the aromatic ring of the starting cyclopropane and formation of a six‐membered carbocycle (Scheme , A ) is the most typical process that can be performed for a wide range of alkenes and acetylenes.…”

“…Acyclic addition involving halide anions (Scheme , C ) is also a process that is highly characteristic of acetylenes. [16a] Of the narrower range of implemented processes, one can note the formal [2+3]‐cycloaddition with participation of allylic systems[16b] (Scheme , B ). Single examples of a number of other implemented processes are also known , …”

Donor‐Acceptor Cyclopropanes in the Synthesis of Carbocycles

“…Moreover, D‐A cyclopropanes have been successfully introduced into dynamic kinetic asymmetric transformations (DYKAT) . These substrates have been also found to react as synthetic equivalents of alkylidene malonates . Based on these advances, total syntheses of diverse natural products from D‐A cyclopropanes have been developed .…”