Synthesis and reactions of lactam sulfonium salts with a sulfonio bridgehead. Part 1. 4,4a,5,6-Tetrahydro-5-oxo-1H-thiopyrano[1,2-a]-1,4-be nzothiazinium perchlorates
Synthesis and reactions of lactam sulfonium salts with a sulfonio bridgehead. Part 1. 4,4a,5,6-Tetrahydro-5-oxo-1H-thiopyrano[1,2-a]-1,4-be nzothiazinium perchlorates
Synthesis and reactions of lactam sulfonium salts with a sulfonio bridgehead. Part 1. 4,4a,5,6-Tetrahydro-5-oxo-1H-thiopyrano[1,2-a]-1,4-be nzothiazinium perchlorates
Tricyclic benzothiazinium salts 3 are prepared by
[2++4] polar cycloaddition of thionium intermediates 2A,
generated from the corresponding α-chloro sulfides 2, and dienes
in the presence of silver perchlorate. Ring transformation of
benzothiazinium salts 3 with a reducing agent such as Mg,
NaBH4 and Zn–AcOH or with a base, furnishes
spiro-vinylcyclopropane derivatives 4 in moderate to high yields.
Electrolysis of 3a at -1.4 V vs. SCE in acetonitrile also
affords vinylcyclopropane 4a (60%). These results indicate that both
ionic and radical mechanisms may account for the vinylcyclopropane
formation, although it is unclear as to the nature of the radical
intermediate. The stereochemistry of 4a was determined by X-ray analysis
showing that sulfur and the vinyl group are cis-orientated.
Ten-membered lactam sulfides 6 are obtained as the major product of
SmI2 reduction of 3.