ON THE MECHANISM OF THE REACTION OF ALPHA-SUBSTITUTED KETONES WITH ALLYLTRIBUTYLSTANNANE

摘要

The mechanisms for the reaction of allyltributylstannane with a number of fragmentation probes, or-substituted acetophenones, were studied. All reactions were shown to proceed through free radical chain sequences since they could be initiated by AIBN and inhibited by m-dinitrobenzene (DNB). alpha-Halo- and alpha-(benzoyloxy)acetophenones (I and II, PhCOCR(1)R(2)X; X = F, Cl, Br, OCOPh; R(1), R(2) = H, Me) yielded the allylation products, PhCOCR(1)R(2)CH(2)CH=CH2), through a chain sequence involving as the propagation step: an electron transfer from Bu(3)Sn(.) to I and II, fragmentation of the ketyl anion PhCOCR(1)R(2)X(.-), and addition of PhCOCR(1)R(2)(.) to allyltributylstannane. The reactions of alpha-(arylsulfonyl)acetophenones (IIIa-c, PhCOCR(1)R(2)Y, Y = SO(2)Tol-p), however, gave a nearly 1:1 mixture of allyl tosyl sulfone and the corresponding ketone, PhCOCHR(1)R(2). The H-1 and C-13 NMR of the reaction mixture between allyltributylstannane and alpha-(p-methylbenzenesulfonyl)-isobutyrophenone substantiated the intermediacy of the tin enolate PhC(OSnBu(3))=CMe(2). These results suggested that a radical addition elimination mechanism was involved in the reactions of IIIa-c with allylstannane. The reaction of alpha-phenylthioacetophenone (IV, PhCOCH(2)SPh) gave both the electron transfer and the addition elimination products (PhCOCH(2)CH(2)CH=CH2, Ph-COCH3), indicating that both pathways were involved in the formation of the products. [References: 34]