Activation of the carbonyl substrate

Among a variety of organotin compounds, allylstannanes, in conjunction with activation of the carbonyl substrates by means of a Lewis acid, are known to be reactive enough for a wide range of synthetic applications. Because excellent and extensive review articles are already available [1], only progress made after publication of these articles is discussed in this chapter (Section 12.2). 

The first activation of the carbonyl substrate by a Lewis acid was reported in 1979 [177] and initiated the increasing use of organotin reagents. The reaction proceeds via an open transition state, as the tin does not compete with the Lewis acid in the coordination of the carbonyl. The diastereoselectivity of the reaction can be induced either by the organometallic or the carbonyl partners. 

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