Aryl groups conjugate additions

Chiral /3,/3-diaryIpropionic acid moieties are often found in compounds showing biological activities, such as antiarrhythmics vasodilators antidepressives " , antihistamines and controllers of cerebral insufficiency ". In the course of synthetic studies of chiral -diaryIpropionic acid derivatives, Merck researchers developed stereoselective conjugate addition of aryllithium reagents to the a,/ -unsaturated fert-butyl esters 18 bearing a chiral imidazolidine or oxazolidine auxiliary at the ortho position of an aryl group. The addition furnished chiral -diaryIpropionic acid derivatives 19 with... 

The sterically unbiased dienes, 5,5-diarylcyclopentadienes 90, wherein one of the aryl groups is substituted with NO, Cl and NCCHj), were designed and synthesized by Halterman et al. [163] Diels-Alder cycloaddition with dimethyl acetylenedicarbo-xylate at reflux (81 °C) was studied syn addition (with respect to the substituted benzene) was favored in the case of the nitro group (90a, X = NO ) (syrr.anti = 68 32), whereas anti addition (with respect to the substituted benzene) is favored in the case of dimethylamino group (90b, X = N(CH3)2) (syn anti = 38 62). The facial preference is consistent with those observed in the hydride reduction of the relevant 2,2-diaryl-cyclopentanones 8 with sodium borohydride, and in dihydroxylation of 3,3-diarylcy-clopentenes 43 with osmium trioxide. In the present system, the interaction of the diene n orbital with the o bonds at the (3 positions (at the 5 position) is symmetry-forbidden. Thus, the major product results from approach of the dienophile from the face opposite the better n electron donor at the (3 positions, in a similar manner to spiro conjugation. Unsymmetrization of the diene % orbitals is inherent in 90, and this is consistent with the observed facial selectivities (91 for 90a 92 for 90b). 

Formation of C-C bonds remains the ultimate challenge to the synthetic chemist. The employment of new synthetic methods in complex target synthesis can be frustrated by a lack of functional group tolerance and substrate specificity. These problems can be somewhat alleviated within conjugate addition reactions by the use of secondary amine catalysts where a number of important and highly selective methods have been developed. Two principle classes of nucleophile have been shown to be effective in the iminium ion activated conjugate addition of carbon nucleophiles to a,P-unsaturated carbonyl systems aryl, heteroaromatic and vinyl... 

Complementary to the use of zinc reagents for the introduction of (functionalized) alkyl groups is the rhodium-catalyzed conjugate addition of aryl- and alkenylboron reagents. This method rapidly became popular, also because arylboron reagents are air and moisture stable and a large variety of them is commercially available . 

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