Lactone synthesis nitrogen nucleophiles

The focus of this review is to discuss the role of Cinchona alkaloids as Brpnsted bases in organocatalytic asymmetric reactions. Cinchona alkaloids are Lewis basic when the quinuclidine nitrogen initiates a nucleophilic attack to the substrate in asymmetric reactions such as the Baylis-Hillman (Fig. 3), P-lactone synthesis, asymmetric a-halogenation, alkylations, carbocyanation of ketones, and Diels-Alder reactions 30-39] (Fig. 4). 

An interesting methodology to highly oxygenated p)razolidines and indolizidines from 2,3-unsaturated sugar lactones was presented by Chmielewski [84]. The synthesis was initiated by a 1,4-addition of nitrogen nucleophiles to unsaturated lactones 93, which resulted in formation of appropriate heterocyclic derivative 94 (O Scheme 38). 

Lactone Formation. There are several exan5)les of the synthesis of lactones with 2-pyridylthiol esters. Since this is a facile reaction, reasonable yields of complex macrocycles are obtained (eq 2). The pyridine nitrogen may provide anchimeric assistance for the approaching nucleophile, thus facilitating the acylation. ... 

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