New heteroaromatic compounds—XIII Reactions of 10-substituted 9-ethoxycarbonyl-10:9-Borazarophenanthrenes

10-Ethoxycarbonyl derivatives of 10:9-borazarophenanthrenes have been prepared by reaction of the 10-lithio derivatives with ethyl chloroformate. Unlike the parent compounds they are rapidly oxidized by air to products in which the BN bond is broken. These reactions suggest that the stability of the present compounds to oxidation and hydrolysis must be due to resonance stabilization. A measurement of the dipole moment of 10-methyl-10:9-borazarophenanthrene by Professor R. Huisgen and his collaborators is reported.