title: Phosphine-catalyzed [4+2] annulations of 2-alkylallenoates and olefins: synthesis of multisubstituted cyclohexenes.
abstract: 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.
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA 90095-1569, USA.
authors: Yang S
authors: YS
authors: Tran
authors: Tioga J
authors: TJ
authors: Martin
authors: Ohyun
authors: O
authors: Kwon
mesh_terms: D000475:Alkenes / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D053138:Cyclohexenes / Q000138:chemical synthesis* / Q000737:chemistry; D010720:Phosphines / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D053138:Cyclohexenes; D010720:Phosphines; C044646:phosphine