Phosphine-catalyzed [4+2] annulations of 2-alkylallenoates and olefins: synthesis of multisubstituted cyclohexenes.

Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA 90095-1569, USA.

Chemistry, an Asian journal 2011 Aug 1

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From our investigations on phosphine-catalyzed [4+2] annulations between α-alkyl allenoates and activated olefins for the synthesis of cyclohexenes, we discovered a hexamethylphosphorous triamide (HMPT)-catalyzed [4+2] reaction between α-alkyl allenoates 1 and arylidene malonates or arylidene cyanoacetates 2 that provides highly functionalized cyclohexenes 3 and 4 in synthetically useful yields (30-89%), with moderate to exclusive regioselectivity, and reasonable diastereoselectivity. Interestingly, the [4+2] annulations between the α-alkyl allenoates 1 and the olefins 2 manifested a polarity inversion of the 1,4-dipole synthon 1, depending on the structure of the olefin, thus providing cyclohexenes 3 exclusively when using arylidene cyanoacetates. The polarity inversion of α-alkyl allenoates from a 1,4-dipole A to B under phosphine catalysis can be explained by an equilibrium between the phosphonium dienolate C and the phosphorous ylide D. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Citation

Yang S Tran, Tioga J Martin, Ohyun Kwon. Phosphine-catalyzed [4+2] annulations of 2-alkylallenoates and olefins: synthesis of multisubstituted cyclohexenes. Chemistry, an Asian journal. 2011 Aug 1;6(8):2101-6