The Decomposition of β-Phenethylsulfonyl Azides. Solution Chemistry and Flash Vacuum Pyrolysis

Article abstract of DOI:10.1021/ja00396a039

The intramolecular cyclization of the parent title compound and a number of para-substituted derivatives (1) in solution was found to take place in low yield and to be accompanied by products of intermolecular reactions, namely, C-H insertion (4) and hydrogen abstraction (3).The use of an excess of a relatively inert solvent Freon 113 led to a better yield of the desired 3,4-dihydro-2,1-benzothiazine 2,2-dioxides (2).Flash vacuum pyrolysis (FVP) of 1 at 250-300 deg C also gave some 2, but the use of higher temperatures led to the formation of styrenes (8), indolines (9), indoles (10), sulfur dioxide, and the remarkable transformation products, the 4-substituted 6,7-dihydro-5H-1-pyrindines (7), in good yield.The styrenes result from the elimination of HN3 and SO2 from the azides, and indolines are formed in good yield by FVP of 2 at 650 deg C.The dihydropyrindines are not obtained from 2, and β-phenethynitrene is not a source of any of the above observed products.A mechanism is proposed for the formation of 7 from β-arylethylsulfonylnitrenes.Consistent with the mechanism is the observation that both 1- and 2-phenylpropanesulfonyl azide give a mixture of 6- and 7-methyl-6,7-dihydro-5H-1-pyrindines in the same ratio on FVP at 650 deg C.Thermolysis of 1a in benzene at 100 deg C gives an N-sulfonylazepine derivative.The FVP of 1 and 2 at 650 deg C are preparative routes to 7 and 9, respectively.