Synthesis of 3,5-disubstituted pyrazole derivatives with a carbamate function

1,3-Dipolar Cycloaddition Reactions of Vinylidenecyclopropane-Diesters with Aromatic Diazomethanes Generated in Situ

“…Diazo compounds are remarkably versatile building blocks in organic synthesis, which are known to take part in 1,3-dipolar cycloaddition reactions with a wide range of dipolarophiles, although they are also known to be toxic and potentially explosive. Recently a new method based on the Bamford−Stevens reaction has been reported for generating aromatic diazomethanes from stable tosylhydrazone derivatives in situ, which has proven to be a highly effective and safe alternative to handling aryldiazomethanes and has been employed in the sulfur ylide-mediated synthesis of epoxides from carbonyl compounds, aziridination of imines, cyclopropanation of alkenes, homologation of aldehydes, Wittig reactions, and preparation of pyrazoles via [3+2] cycloadditions with alkenes and alkynes . Vinylidenecyclopropanes (VDCPs) as highly strained small rings have an allene moiety connected by a cyclopropane.…”