“…The nucleophilic attack by an external reagent at the g position of XXVIII is an interesting possibility because it represents a 4 umpolung reactivity of the starting alkynoate. [123] In the case of alcohols, [124] amines, [125] carboxylic acids, [126] malonates, [127] glycine imines, and nitroalkanes, [128] g addition to XXXV or XXXVI occurs to give products 84 or 85, respectively (Scheme 29). [129] The g addition of bifunctional reagents such as diols, diamines, and amino thiols leads to novel methods for the phosphane-catalyzed synthesis of thiazoles, dihydrofurans, and a variety of other heterocycles.…”