1.3- Dioxolium-4-olates

The first synthesis of 1,3-dioxolium-4-olates (here defined as oxamiinchnones) was reported in 1980 by Berk et al. (64) but it was work of Hamaguchi and Nagai (65,66) that demonstrated the accessibility and utility of these new mesoionic heterocycles in cycloaddition reactions. Thus, reaction of diazoacetic benzoic anhydrides 108 with a 7t-allyl palladium complex affords oxamiinchnones 109. 

The main methods available to prepare 1,3-oxathiolium salts and their mesoionic 4- and 5-olates are of this type and were covered in CHEC-I <84CHEC-I(6)749> but two important new methods have been described. The 2-amino-1,3-oxathiolium salts (208) can be obtained by desulfurization of the phenacyldithiocarbamates (207) with a silver, mercury, or copper salt (Equation (28)) <92JAP04364178>. The l,3-dioxolium-4-olates (210) have been generated from the a-diazo anhydrides... 

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