Search

A new ionic cyclopropanation process involving the addition of diazo esters to donor-acceptor cyclopropanes (DAC) activated by GaCl3 has been developed. The reactions occur via 1,2-zwitterionic gallium complexes with elimination of nitrogen in all cases to give 1,1,2,3-tetrasubstituted cyclopropanes as the main products. Also, a number of related processes with the formation of various polysubstituted cyclopropanes, alkenes, and cyclobutanes, including products of multiple diazo ester addition, have been developed. Obtained by the developed method tetrasubstituted cyclopropanes are activated cyclopropanes such as DAC and can be used for further synthesis in this capacity. Their new reaction with benzaldehyde promoted by TiCl4 and involving one of the additional functional groups has been demonstrated, which leads to five-membered lactones. The mechanisms of the occurring processes, as well as the structures and stereochemistry of a rich range of products formed, are discussed in detail.

The reactions of 1,2-zwitterionic complexes, generated from 2-arylcyclopropane-1,1-dicarboxylates (ACDC) or benzylidenemalonate and gallium trichloride, with benzyl azide proceeds as a formal [3+2] cycloaddition to form dihydro-1,2,3-triazoles. The latter, when the reaction mixture is treated with 10% aqueous HCl, undergo retrocyclization with elimination of diazomalonate. The reaction of ACDC, benzyl azide, and GaCl3 with simultaneous mixing of the reagents leads to the interception of the 1,3-zwitterion, with this stage being accompanied by both the cyclization to substituted 1,2,3-triazinine and the elimination of a nitrogen molecule to form 3,4-dihydro-2H-1,2-oxazine structure, which after acid hydrolysis gives substituted 3-hydroxypyrrolidin-2-one.

2-Styrylcyclopropane-1,1-dicarboxylate treated with anhydrous gallium trichloride undergoes dimerization with the cyclopropane ring opening and the styryl substituent double bond involvement, leading to the formation of polysubstituted cyclic and bicyclic structures with the predominance of the former or the latter depending on the reaction conditions. Most compounds are formed with very high diastereoselectivity. Thirteen major and minor dimeric structures were isolated and reliably characterized, two of which were found to additionally include a chlorine atom. A rare for the reactions of donor-acceptor cyclopropanes example of the formation of a product with the fused cyclobutane ring was effected at–80 °C. Plausible mechanisms of observed processes were discussed.

A new process for isomerization of donor–acceptor cyclopropanes (2-arylcyclopropanedicarboxylates) by treatment with anhydrous gallium trichloride to give (2-arylalkylidene)malonates in high yields and with good selectivity has been developed. The reaction involves initial formation of a 1,2-dipolar gallium complex.

A new process for the [4 + 2] annulation of donor–acceptor cyclopropanes with acetylenes under the effect of anhydrous GaCl3 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.