ABSTRACT
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 GaHal3 and involves the intermediate in situ generation of 1,2-zwitterionic gallium complexes with [Ga(L)3]3+[GaX4-]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.
ABSTRACT
A new cascade process for reactions of donor-acceptor cyclopropanes (DACs) with spiro[cyclopropanepyrazolines] in the presence of EtAlCl2 or Ga halides is reported. The action of a Lewis acid results in DAC activation and addition of the carbocationic intermediate to the azocyclopropane system of the pyrazoline with opening of the second three-membered ring and addition of a halide anion from the Lewis acid. A specific feature of this process is that one activated cyclopropane ring activates another one, and depending on the component ratio, the process can involve two DAC molecules and one pyrazoline molecule or one DAC molecule and two pyrazoline molecules. The process is tolerant to various functional groups and occurs with a wide range of substrates to give polyfunctionalized structures based on a 2-pyrazoline moiety.
ABSTRACT
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.
ABSTRACT
A new process for (4 + 2)-annulation of donor-acceptor cyclopropanes (DACs) with unsaturated compounds in the presence of anhydrous GaCl3 has been developed. In this process, DACs act as sources of formal 1,2- and 1,4-dipoles to give polysubstituted tetralins in high yields and with high regio- and diastereoselectivity. Alkenes with both aryl and alkyl substituents at the double bond undergo this reaction equally readily. A most likely mechanism of the reaction has been proposed. It involves preliminary generation of a key 1,2-dipolar gallium complex and its subsequent participation in annulation with an alkene.
Subject(s)
Alkenes/chemistry , Cyclopropanes/chemistry , Gallium/chemistry , Tetrahydronaphthalenes/chemistry , Catalysis , Cycloaddition Reaction , Molecular Structure , Oxidation-Reduction , StereoisomerismABSTRACT
A new type of donor-acceptor cyclopropane reactivity has been discovered. On treatment with anhydrous GaCl3 , they react as sources of even-numbered 1,2- and 1,4-dipoles instead of the classical odd-numbered 1,3-dipoles due to migration of positive charge from the benzyl center. This type of reactivity has been demonstrated for new reactions, namely, cyclodimerizations of donor-acceptor cyclopropanes that occur as [2+2]-, [3+2]-, [4+2]-, [5+2], [4+3]-, and [5+4]-annulations. The [4+2]-annulation of 2-arylcyclopropane-1,1-dicarboxylates to give polysubstituted 2-aryltetralins has been developed in a preparative version that provides exceedingly high regio- and diastereoselectivity and high yields. The strategy for selective hetero-combination of donor-acceptor cyclopropanes was also been developed. The mechanisms of the discovered reactions involving the formation of a comparatively stable 1,2-ylide intermediate have been studied.
