Crotyltin reagents

Unfortunately, substitution in the y-position, such as in crotyltin, led to poorly reactive allyltins, due to the decrease in the addition rate of the radicals to the double bond. It has been established that, generally, the competitive allylic hydrogen abstraction became predominant, destroying the crotyltin reagent ". The use of y-substituted allyltins for the photo-induced radical allylation of carbonyl compounds represents an interesting... 

Silver BINAP complex was used as well by Yanagisawa and coworkers . The particular feature of this catalyst is the marked anti selectivity when nsing crotyltins, regardless of whether the donble bond is (E) or (Z). This selectivity is explained by a fast transmetaUation step between the chiral complex and the organotin reagent, followed by the addition on the carbonyl gronp via a cyclic transition state. This reaction has been extended to other organometallics snch as 2,4-pentadienylstannanes . 

It was demonstrated that BINOL catalysts authorize the /3- and /-functionalizations of the allyltin reagents without lowering the enantioselectivity level [223], and such a strategy was used in the total syntheses of macrolides [224] or substituted tetrahydropyran units [225]. It was noteworthy that the BINOL-Ti catalysis was extended to the enantioselective allylation of alkyl and aromatic ketones in good yields with up to 96% ee [226]. Silver/BINAP was used as well, with a marked anti selectivity, when using crotyltins whatever is the nature, (E) or (Z) of the double bond [227]. This reaction was extended to other organometallics such as 2,4-pentadienylstannanes [228] or buta-2,3-dienylstannanes [229] (Scheme 6.26). 

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