Thermal rearrangements of azathiabenzenes; [1,4] shifts in cyclic sulphur–nitrogen ylides

Abstract

The azathiabenzene derivatives (3), ( 7 ) , and (1 I) rearrange on heating by a [I ,4] shift of the sulphur substituent to carbon rather than a [I ,2] shift to nitrogen, even though for ylides (3) this rearrangement involves loss of thiophen and furan aromaticity.

Synthesis of prazolinones from β-N,N-dimethylhydrazinopropenoates: an example of a thermally induced [1,4] alkyl shift

“…The synthesis of pyrazolinones from P-hydrazinopropenoates, since it requires a hydrogen atom on the terminal nitrogen atom of the hydrazine group,l cannot be carried out with N,N-dialkyl derivatives such as (1). We are currently studying the thermal behaviour of p-enaminoesters and we now report that flow pyrolysis of compounds (l), in toluene, gives facile access to pyrazolinones (2) through the intermediacy of pyrazolinium ylides (3). We believe that the last step of the reaction is the first known example of a [1,4]…”