Group transfer-type additions

The greater activity of LiC104 (3 mol %)-CH2Cl2 enables conjugate addition of Si-2 to 12. Complete and regioselective conversion to the desirable 1,4-adduct was, in fact, achieved within 1 h >91 % isolated yield), presumably via a group transfer-type process (Sch. 60) [72]. 

Group transfer-type of Mukaiyama aldol addition to aldehydes or ketones affords the isolable 0-silylated aldol adducts, which can be hydrolyzed under acidic conditions to provide a-keto esters in high yield (eq 2) In the case of aldehydes the initial products are 0-silyl-protected reductones. ... 

Another type of mixed cyanocuprate has both methyl and alkenyl groups attached to copper. Interestingly, these reagents selectively transfer the alkenyl group in conjugate addition reactions.16 These reagents can be prepared from alkynes via hydrozirconation, followed by metal-metal exchange.17... 

The exceptional nucleofugality of the phenyliodonio group has been determined in an alkenyl salt and it is about 106 times greater than that of triflate [30]. This remarkable property makes alkenyl iodonium salts excellent vinyl cation equivalents in nucleophilic substitutions. The chemistry of alkenyl iodonium salts is dominated by the transfer of their aliphatic moiety to a variety of nucleophiles other important reactions involve Michael-type addition and alkylidenecarbene generation, along with elimination to alkynes which is actually an undesirable side-reaction. 

Acyl radical sources, other than aldehydes, are also available. The group transfer addition of an acyl radical has been reported by Zard and co-workers, where S-acyl xanthates serve as acyl radical sources [44]. Crich and co-workers reported that an acyl radical, generated from an aromatic acyl telluride by photolysis, adds to an allylic sulfide which contains an ethoxycarbonyl group to form the corre-.sponding y-unsaturated ketones [45]. The addition pathway involves Sh2 type reaction with extrusion of a /ert-butylthiyl radical. 

Asymmetric addition of allylmetals to carbonyl compounds is also a well-represented reaction type. Several A-oxides (54 55A ) are found to be effective catalysts for group transfer from allyltrichlorosilane and allylstannanes. 

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