Ionic Ga-Complexes of Alkylidene- and Arylmethylidenemalonates and Their Reactions with Acetylenes: An In-Depth Look into the Mechanism of the Occurring Gallium Chemistry

Abstract

A new synthetic concept was suggested in the chemistry of substituted methylidenemalonates that enables their utilization as 1,2-zwitterionic synthons. This strategy is to generate liquid ionic Ga complexes from methylidenemalonates and GaHal3 with a strict 3/4 composition and then use them in further synthesis. A number of complexes with different metal halides have been synthesized and studied in detail. The unique properties of gallium among all metals have been demonstrated and explained. On the basis of the discovered new class of gallium complexes of methylidenemalonates, a number of novel reactions with acetylenes have been elaborated, which are unknown in the conventional chemistry of methylidenemalonates. The main demonstrated process is a three-component addition to a triple bond involving halide anions, leading to the formation of polyfunctional vinyl halides with high E-selectivity. The mechanism has been studied experimentally in fine detail. Application of specially optimized 71Ga NMR spectroscopy makes it possible to take an in-depth look into the gallium chemistry in a new light. In particular, the key participation of GaHal4 – anions in the occurring transformations has been established.

Dumbbell‐Shaped, Graft and Bottlebrush Polymers with All‐Siloxane Nature: Synthetic Methodology, Thermal, and Rheological Behavior

“…The study of the structure of the obtained compounds on the example of a graft polymer 5‐G 1 (Et) with Et 3 SiO‐labelling group in pendant using a complex of 2D NMR methods is one of the most indicative and illustrative ( Figure ). [ 61–64 ] This is because EtSi‐groups are not overlapped with all MeSi‐groups and clearly indicate the structural positions of the G 1 (Et) ‐fragment in pendant. 1 H DOSY in combination with NOESY spectra show complete attachment of all G 1 (Et) ‐fragments with a narrow MW distribution of the target polymer, all EtSi‐groups have exactly the same diffusion coefficients as for PDMS chain (see p. S22, Supporting Information for detailed explanation).…”

Catalytic Cycloisomerization of Enyne Diesters Derived From 2‐Propargyloxyarylaldehydes

“…[18,19] Yamazaki et al reported an elegant intramolecular cycloisomerization of enyne triester of type 3 to compound 4 using stoichiometric amount of ZnBr 2 as the promoter and THF as an additive (Scheme 1b). [20] Recently, Novikov, Tomilov and co-workers demonstrated a new synthetic concept of utilizing dialkyl 2-arylidene malonates as 1,2zwitterionic synthons [21] in the presence of stoichiomet-ric amount of gallium halides. The reaction has broad synthetic utility and provides access to diverse molecular scaffolds including lactones and indenes.…”

“…Thus, in an intermolecular reaction of electrophilic olefin 5 with nucleophilic alkyne 6 in the presence of stoichiometric amount of gallium halide produced compound 7 stereoselectively (Scheme 1c). [21] Inspired by these recent literature reports, [7,10,21] we planned to develop a catalytic intramolecular cycloisomerization reaction of enyne diesters derived from 2-propargyloxyarylaldehydes. We envisioned that enyne diester type 8 upon treatment with catalytic amount of a suitable metal catalyst bearing non-nucleophilic ligands (such as triflate) would generate 1,2-dipole intermediate 9 (Scheme 2a).…”

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

“…Nevertheless, a few processes of four‐membered ring formation in DAC reactions with multiple C–C bonds are known to date[14a], (Scheme , pathways A , B–D , E ). All of them corresponded to the 1,2‐zwitterionic chemistry of DAC and occurred only as side processes and in low yields.…”