Tungsten(0) alkylidene complexes stabilized as pyridinium ylides:: new aspects of their synthesis and reactivity

The interaction of dihydropyridines with alkoxycarbene complexes of tungsten has been shown to lead to pyridinium ylid complexes: this transformation has now been applied to the synthesis of a hydroxyl-containing ylid complex by ring-opening of the pentacarbonyl (2-oxacyclopentylidene) tungsten(0) complex and to the synthesis of a series of chiral ylid complexes both from chiral and non-chiral carbene complexes by the use of dihydropyridines and dihydronicotines, respectively. The transfer of the alkylidene moiety of these complexes to nucleophilic olefins will be outlined and discussed. Especially relevant is the interaction of these pyridinium ylid complexes with unsaturated substrates such as dihydropyridines, enamines, and beta -alkoxy bis(trimethylsilyl) ketene acetals. This latter reaction leads to conjugated carboxylic acids, and has been be applied to a new synthesis of a honey bee pheromone, the queen substance. (C) 2001 Elsevier Science B.V. All rights reserved.