Chemoselective Michael and Aldol Reactions

Dibutyltin bis(triflate), Bu2Sn(OTf)2, is a mild Lewis acid which catalyzes clean Michael addition of enol silyl ethers [148]. The new catalyst enables use of various labile acceptors such as methyl vinyl ketone and 2-cyclopentenone which do not undergo smooth reaction with conventional Lewis acids. A variety of enol silyl ethers are also employable and thus 2-(trimethylsiloxy)propene, the simplest of this class of compounds, can be used. The adducts of enol silyl ethers of cycloalkanones with vinyl ketones are readily cyclized to give the desired annulated enones free of isomers. Consequently, a practical version of the Robinson annulation has been realized. 

8-Bis(allyldibutylstannyl)naphthalene is highly effective for the selective allylation of aldehydes and ketones under neutral conditions (Eq. 112) [151]. Such a transformation is not realized with monostannane. The former reaction proceeds without any catalyst by taking advantage of the chelation-induced Lewis acidity of bidentate bis(stannyl) compounds. 

Lange s Handbook of Chemistry, 3rd Edn, McGraw-Hill, New York, 1985, p. 3. 

Oriyama, X Iwanami, K. Tsukamoto, K. Ichimura, Y Koga, G. Bull. Chem. Soc. Jpn 1991,64,1410. Yamaguchi, J. Takagi, Y Nakayama, A. Fujiwara, X. Xakeda, X. Chem. Lett. IWl, 133. 

Donaldson, J. D. Progress in Inorganic Chemistry, Cotton, F. A., Ed. Vol. 8. John Wiley, New York, 1967, p 287. 

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