Lactones synthesis, asym

A. P. Rauter, J. A. Figueiredo, I. Ismael, T. Canda, J. Font, and M. Figueiredo, Efficient synthesis of a,/ -unsaturated /-lactones linked to sugars, Tetrahedron Asym., 12(2001) 1131-1146. 

The facial selectivity of (43) was found to be 1.75 1 from the ratio of aldol products (48) and (49) obtained by the reaction with the achiral boron enolate (50). The latter is structurally similar to reagents (37) and (38). These experiments confirm again the validity of the rule of double asymmetric synthesis. The product (44) can be further converted through a sequence of reactions to provide (+)-Prelog-Djerassi lactonic acid (51 Scheme 27) (i) trimethylsilylation (ii) hydroboration with thexylborane (single asym-... 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

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