Stannanes reactions

A virtue of the silane donors is that they avoid the by-products of stannane reactions, which frequently cause purification problems. 

SnCU is effective in promoting the addition of nucleophiles to simple aldehydes. Among the most synthetically useful additions are allylstannane and -silane additions. The product distribution in the stannane reactions can be influenced by the order of addition, stoichiometry, and reaction temperature. The anti geometry of the tin-aldehyde complex is favored because of steric interactions. Furthermore, the six-coordinate 2 1 complex is most probably the reactive intermediate in these systems. The use of crotylstaimanes provides evidence for competing transmetalation pathways (Eq. 35) [60]. TiCU results in superior selectivity. 

The addition of allenylstannanes to aldehydes bears many similarities to the allyl-stannane reactions. All of the same stereochemical issues are relevant and have been addressed. Mechanistically, there are also strong re.semblances and finally these reactions have been used successfully as a key transfonnation in the total synthesis of several natural products [104]. The reaction proceeds in high yield and excellent regio- and stereoselectivity to afford the desired homopropargylic alcohols. 

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