Fascinating problems in organic reaction mechanisms-VII 1: novel sodium nitrite-aqueous acid cis-hydroxylation reaction

Abstract

Tetraphenylcyclopentadienone 1 is transformed in 85% yields to the cis diol 2 with sodium nitrite-aqueous acetic acid, under conditions usually employed for deamination. This change, and clean cis-hydroxylation of tetramethyl cyclobutadiene constitute notable examples of cis-hydroxylation with sodium nitrite-aqueous acid. Reactions of tetracyclone with dinitrogen trioxide, dinitrogen tetroxide, dinitrogen pentoxide, nitrous acid and nitric acid show that nitric acid is the reagent involved in cis-hydroxylation. Unknown facets related to the chemistry of oxides of nitrogen, the most significant being the existence of the olefin + N₂O₃⇔ adduct equilibrium have been revealed, and the chemistry of the adducts has been studied. Of a variety of substrates examined, only dienes respond to the sodium nitrite-aqueous acid reagent. The minimum requirements for the reaction are that the substrate be a good diene and that the initially formed [4 + 2] adduct shall decompose by a C-N bond rupture. A similar sequence explains the fascinating transformation of tetracyclone to pentaphenyl pyrrole in boiling nitrobenzene.