The synthesis of 1H- and 5H-thieno[1,2]diazepines by the electrocyclisation of α-(2-alkenylthienyl)diazoalkanes, and some observations on their photochemical reactivity and ring inversion

A Convenient Synthesis of Symmetric 1,2-Diarylethenes from Arylmethyl Phosphonium Salts

“…The phosphonium salts (except 6 , which was obtained commercially) were synthesized from the corresponding methylthiophenes. The methylthiophenes were brominated with N -bromosuccinimide in the presence of benzoyl peroxide, and then treated with triphenylphosphine. , For the synthesis of compound 4 , 3-methylthiophene was first nitrated, using literature procedures, followed by bromination and treatment with triphenylphosphine.…”

Electrocyclic aromatic substitution by the diazo group. Part 5. The reactions of α-(2-arylthienyl)diazoalkanes

“…This work is concerned with diazo-compounds of types ( 1) and ( 2) and was carried out as part of our programme investigating the reactions of 1,3-dipolar intermediates conjugated with systems of 4 x electrons. Two pieces of earlier work provide the background : (i) diazo-compounds of types (3) and (4), analogous to (1)/(2) but having an alkenyl rather than aryl double bond in the y, 6 position, cyclise readily via an 8x electron 1,7 electrocyclisation to give thieno [ 1,2]diazepines, e.g. (6) from (3),' (ii) diazo-compounds of type (7), analogous to (1)/(2) but having a cyclopentenyl rather than a thiophene ring, undergo ring closure by both 8x and 6.n electron cyclisations to give the 1,2-benzodiazepine (9) and the pyrazole (8)-which rearranges thermally to give (9)-and some (ca.…”

“…(6) from (3),' (ii) diazo-compounds of type (7), analogous to (1)/(2) but having a cyclopentenyl rather than a thiophene ring, undergo ring closure by both 8x and 6.n electron cyclisations to give the 1,2-benzodiazepine (9) and the pyrazole (8)-which rearranges thermally to give (9)-and some (ca. 20%) carbene-derived product ( The reactions of ( 1) and (2) were studied in the hope that they would undergo 1,7 electrocyclisation and so provide a direct route to fused 1,2-benzodiazepine systems such as (1 2) and ( 13) which are structurally similar both to (14) and to a large range of fused 1,4-benzodiazepine systems such as (1 5 ) which have proved to be highly effective CNS agents.…”