Allylic substitutions organozinc reagents

Condensation of sulfoximine 717 with an aldehyde and benzotriazole produces Ar-[ -(bcnzotnazol-l -yl)alkyl]sul-foximine 718. Treatment with allyl silanes in the presence of BF3 etherate or with organozinc reagents allows substitution of the benzotriazolyl moiety in compound 718 to produce variety of substituted sulfoximines 719... 

Scheme 6.42. Copper-catalyzed allylic substitution of mesylate 197 with an organozinc reagent.

Direct substitution reaction of 125 <1995EJM697> with organozinc reagents derived from allyl, benzyl, phenyl, vinyl, and -butyl Grignard reagents stereoselectively produced C-lO-substituted deoxoartemisinins 142 in good to moderate yields (Scheme 17 Table 12) <2002TL2891>. 

Besides the issues associated with the regioselectivity and stereoselectivity of these reactions, there is also one particular point of consideration in the case of substituted allylic organozinc reagents which deals with the metallotropic equiUbrium of such species. Indeed, each regio- or stereoisomer of a substituted allylic organozinc can in principle give rise to a different carbometallation product. 

As 1,2-disubstituted triple bonds do not generally react with allylic organozinc reagents, conjugated terminal diynes underwent chemoselective allylzincation at the terminal alkyne moiety leading to allyl-substituted conjugated enynes (equation 138)173. 

The stereochemistry of addition of an allylic organozinc reagent to a carbonyl group has received considerable attention. Both diallyl- and dicrotylzinc in their reactions with alkyl-substituted cyclohexanones display a strong preference for equatorial attack (formation of the rfl -alcohol) on the carbonyl group (5, 6), e.g.,... 

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