Morita-Baylis-Hillman Reaction of α,β-Unsaturated Ketones with Allylic Alcohols by the Combination of Transition-Metal Catalysis and Organomediation

Abstract

The Morita-Baylis-Hillman (MBH) reaction of α,β-unsaturated carbonyl compounds with allylic halides or allylic esters has been reported. Compared with allylic halides and allylic esters, allylic alcohols are usually more easily prepared. However, to the best of our knowledge, there is no systematic results on the MBH reaction of α,β-unsaturated carbonyl compounds with allylic alcohols. Our experimental results demonstrated that by the catalysis of 10 mol% Pd(PPh 3 ) 4 and the mediation of 100 mol% P(n-Bu) 3 , various aryl vinyl ketones 1a～1g were able to undergo the MBH reaction smoothly with allylic alcohol 2a in the mixed solvents of toluene/(CF 3 ) 2 CHOH (V/V＝35/1) at 60 ℃ under nitrogen, affording desired α-allylated products 3aa～3ga in the yields of 57%～80%. The MBH reaction is compatible with a series of functional groups on the benzene ring in 1a～1g, such as fluoro, chloro, trifluoromethyl, methyl, and methoxyl group. Naphthyl group instead of benzene group in aryl vinyl ketone 1h also led to α-coupling product 3ha in a good yield. Various 3-aryl allylic alcohols 2b～2f were also able to undergo the MBH reaction smoothly with vinyl ketone 1b, affording the desired α-allylated products 3bb～ 3bf in good yields with excellent regioselectivities and E-selectivities. 2-Methylprop-2-en-1-ol (2g), 1-phenylprop-2-en-1-ol (2h) or 1,3-diphenylprop-2-en-1-ol (2i) also performed the MBH reaction expediently with vinyl ketone 1b to give the corresponding α-coupling product 3bg, 3bb, or 3bi. A plausible mechanism using (CF 3 ) 2 CHOH to both form phosphonium salt 4 and activate allylic alcohols was also proposed. The MBH reaction has many advantages, such as easy availability of starting materials, good tolerance to many functional groups, excellent regioselectivities and E-stereoselectivities, and satisfactory yields. Thus the MBH reaction of aryl vinyl ketones with allylic alcohols may have practical applications in organic synthesis or industry in the future.