82777-77-3Relevant articles and documents
Inversion de polarite par les groupes phosphore: inversion de regioselectivite dans l'addition des nucleophiles sur les allenes actives par des groupes attracteurs
Cristau, Henri-Jean,Viala, Jacques,Christol, Henri
, p. 980 - 998 (2007/10/02)
Change in the regioselectivity of the addition of nucleophilic compounds YH (ROH, RSH, RNH2) on α-allenic ketones and esters can be effected by using the triphenylphosphonio group as an umpolung agent.In this way α,β-unsaturated ketones and esters are obtained with heteroatomic substituents in the γ position.The umpolung scheme of the activated allene is characterized by a vinylphosphonium salt 7 or 10 as a synthetic equivalent of the a4 synthon .CH2-CH=CH-Z.The synthetic process requires three (Z = COCH3) or two (Z = CO2CH3) distinct manipulations and gives good overall yields (63 to 71percent).This umpolung method can also be applied to binucleophilic compounds as a new synthesis for functional heterocycles such as the substituted dioxan 15c or pyrrole 16d.Two separate side reactions of the intermediary phosphonium salts were found to occur: a) the isomerization of the vinylphosphonium salts with migration of the double bond, and, b) for β-substituted phosphonium salts, exchange of heteroatomic groups Y through elimination-addition.Both side reactions can however be completely controlled.
