Diastereoselectivity exocyclic substituents

If the enone is part of a decalone system, i.e., a / - and an y-substituent are present, on reaction with lithiated areneacetonitriles in THF the exclusive formation of (Tv-substituted decalones is observedl26. The diastereoselectivity at the exocyclic stereogenic center is, however, poor. Applications in the synthesis of anthracyclines are given in the literature127,12S. 

Indium-mediated allylation of c -keto-/3-lactams such as 6-oxopenicillanate and 7-oxocephalospranate proceeds diastereoselectively to afford a-allyl-/3-lactams in aqueous media (Scheme 42). In the cinnamylation of the mono-cyclic compound, the diastereofacial selectivity is directly linked to the (R)- or (A)-configuration of the exocyclic A-substituent (Scheme 43).175,176-180... 

Aliphatic enamine derivatives 198 linked to a chiral oxazolidone allow an almost totally diastereoselective [2 + 2] photocycloaddition of 102 (Scheme 53). This efficiency was attributed to a selective shielding of the lower face by the R substituents in the preferred conformation of the chiral oxazilidone enecarbamate. Interestingly, the de of 199 did not depend on the configuration of the stereocenter on the exocyclic appendage [122]. 

Although there are only a few examples of alkylations of carboxylate enolates which are exocyclic to five-membered carbocyclic rings, the usual steric factors seem to control the stereoselectivity of these reactions. Thus, the dienolate (111) underwent reaction with 4-bromo-l-butene anti to the methoxymethyl substituents with high diastereoselectivity " and enolates derived from norbomane-2-carboxylates (112)... 

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