The Cp 2 ZrCl 2 catalyzed cycloalumination of acetylenic alcohols and propargylamines by Et 3 Al was studied. The process affords 2,3 disubstituted alumacyclopent 2 enes, which were identified by the analysis of the products of their deuterolysis and hydrolysis. The cycloalumi nation of alkyl and phenyl substituted propargylamines proceeds with high regio and stereo selectivity to give the corresponding allylamine derivatives in high yield. Unlike the phenyl derivatives, the cycloalumination of alkyl substituted acetylenic alcohols (propargyl, homopro pargyl, and bishomopropargyl alcohols) is not regioselective.Among numerous methods of synthesis of organoalu minum compounds, the reactions of hydro , carbo , and cycloalumination of olefins and acetylenes found the wid est use. 1 However, the first two methods are well studied both methodologically and theoretically, while cycloalu mination is relatively new promising direction that re quires the study of boundaries of application of this reac tion and its mechanism. We have earlier 2 reported the synthesis of substituted alumacyclopent 2 enes from alkyl and phenyl substituted acetylenes. It was found 3 that the cycloalumination of nonsymmetric alkyl , phenyl , and allyl substituted acetylenes by Et 3 Al affords regioisomeric 2,3 disubstituted alumacyclopent 2 enes, whose yield and ratio depend on the nature of substituents in the starting acetylenes.In order to extend the area of application of the above cycloalumination reaction and taking into account the important role of various functional substituents in the induction of biological activity, in the present work we studied the regularities of the reaction with acetylenic alcohols and amines.
Results and DiscussionCycloalumination of propargyl alcohols. At room tem perature propargyl alcohols are not almost involved in cycloalumination. For instance, in the reaction of hept 2 ynol with Et 3 Al (the mole ratio of the reactants is 1 : 3) in hexane in the presence of 10 mol.% Cp 2 ZrCl 2 at room temperature, the conversion of the starting propargyl alcohol after 24 h does not exceed 5%. However, the rise of the reaction temperature to 40 °С and an increase in the catalyst concentration to 20 mol.% favor the formation of alumacyclopent 2 enes. In the case of alkyl substituted propargyl alcohols (hept 2 ynol, non 2 ynol), cycloalu mination followed by deuterolysis affords deuterolysis products 1a,b in 37 and 41% yields, respectively (Scheme 1). The reaction occurs stereoselectively to form substituted allyl alcohols of the Z configuration. The cycloalumina tion of 3 phenylprop 2 ynol requires more rigid condi tions and the use of 3 molar equivalents of Et 3 Al over propargyl alcohol. However, the reaction product is formed with high regio and stereoselectivity and in a higher yield (60%) compared to alkyl substituted propargyl alcohols. Scheme 1 R = Bu (1a), C 6 H 13 (1b, 2a), Ph (1c, 2b)