Overview of Chiral Allylmetal and Allenylmetal Reagents

These selected synthetic applications of the ring-closing allylation reaction illustrate the opportunities for obtaining with high stereoselectivity functionalized heterocycles and carbocycles, common units found in natural products. Other applications of intramolecular allylation reactions have been reported [95-101, 103]. 

In the following Sections we review the reactions of chiral allylmetal and allenylmetal reagents and their application to the synthesis of complex natural products. These reagents are useful for the enantioselective allylation of achiral aldehydes 

Methods for the preparation of, 2-syn diol adducts using chiral y-(alkoxyal-lyl)boron reagents 228 [164] and 229 [165], and (y-alkoxyallyl)stannane reagents 230 [166-168], 231 [169] and 232 [170], have been reported (Fig. 11-20). 

Reagents developed for the synthesis of 2-anti diol adducts include the chiral [( )-7-alkoxyallyl]indium and [( )-7-alkoxyalIyl]boronate reagents 233 [171J and 234 (Fig. 11-21) [172]. Alternatively, the ( )-allylboron reagents 235-237, which included silicon and boron substituents as hydroxy sunogates, have been independently developed [173-177]. 

Of these reagents, Brown s reagent 229 and Marshall s reagents 230 and 233 have been used most extensively for appending diol units in natural product. syn- 

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