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.

A new process for the [4 + 2] annulation of donor-acceptor cyclopropanes with acetylenes under the effect of anhydrous GaCl using 1,2-zwitterion reactivity was elaborated. The reaction opens access to substituted dihydronaphthalenes, naphthalenes, and other fused carbocycles. The direction of the reaction can be efficiently controlled by temperature.

A new approach was suggested for the development of new carbon-based synthons on donor-acceptor cyclopropane (DAC) basis, that are more complex than the usual cyclopropane ring, while maintaining the principle of separation of donor and acceptor substituents in the molecule. This approach is based on expansion of the reactive cyclopropane ring system in DACs by inserting into the structure the additional reactive CÀC double bond or the second cyclopropane ring between donor and acceptor substituents. Within this approach and applying a set of procedures adopted in cyclopropane chemistry, the new (2-phenylcyclopropyl)methylidenemalonate (3) and related 2 '-phenylbicyclopropyl-1,1-dicarboxylate (2) were synthesized as vinylog and homovinylog of donor-acceptor cyclopropanes. Upon studying their reactivity, focusing on their transformations in the presence of various Lewis acids, the bicyclopropyl skeleton in 2 behaved as a single six-carbon synthon, in which both cyclopropane rings reacted in tandem furnishing various products with opening of the cyclopropane rings. On the other hand, the vinylcyclopropane 3 turned out to be much less reactive towards the same Lewis acids. Mechanistic aspects, further transformations of the ring-opened products and potential synthetic applications of these new reactions in organic synthesis are being discussed as well.

A new cascade three-component process for high trans,trans-diastereoselective assembly of five-membered (1-halovinyl)lactones has been developed. The process is based on reactions of substituted methylidenemalonates and cyclopropanedicarboxylates with 3-haloprop-1-ynes in the presence of GaHal 3 and involves the intermediate in situ generation of 1,2-zwitterionic gallium complexes with [Ga-(L) 3 ] 3+ [GaX 4 − ] 3 composition. Chloro, bromo, and iodo derivatives can be obtained successfully. Mechanistic and stereochemical aspects of the process we developed have been studied and considered in detail.

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