Cu(II)-Catalyzed Allylic Silylation of Morita–Baylis–Hillman Alcohols via Dual Activation of Si–B Bond and Hydroxyl Group (original) (raw)

2013, The Journal of Organic Chemistry

silylation of allylic alcohol via dual activation of Si-B bond and hydroxyl group of the MBH alcohol provided an efficient and convenient method for the synthesis of functionalized allylsilanes. Allylsilanes are important synthetic reagents, and have been applied widely in the synthesis of natural products and bioactive compounds. 1 Many efficient methods for the synthesis of allylsilanes have been developed through the silylations of allylic substrates by silylmetal reagents (silylmagnesium, silyllithium, silylcuprate, and silylzincate etc). 2 Recently, attentions have been focused on the uses of interelement silicon-boron reagents for the synthesis of functionalized silanes. 3 Under mild conditions, silicon-boron reagents allow the catalytic transfer of a silicon nucleophile onto various electrophiles. Activation of the Si-B bond could be catalyzed by various transition-metals (such as Pd(0), 3a,4 Rh(I), 3a,5 and Cu(I) complexes) 3a,6 and N-heterocyclic carbenes, 7a or activated by the substrate itself, 7b to generate a silicon nucleophile. Oestreich and co-workers reported the allylic substitution of allylic precursors with Si-B compounds catalyzed by CuCN/NaOMe. 8 However, the allylic precursors were confined to the functionalized allylic compounds such as allyl halides, allyl esters, allyl carbonates, and allyl phasphonates. For synthetic efficiency, it is much more desirable to generate allylsilanes directly from allyl alcohols. Although the direct substitution of alcohols with carbon and heteroatom nucleophiles is a significant chemical transformation, 9 the direct synthesis of allylsilanes from allylic alcohols has seldom been reported due to the poor leaving ability of hydroxyl group.