Gerhard Maas

Unusual oxygen shift during dimerization of λ5σ3-phosphaalkynes

Abstract The phosphaalkynes 7 - generated by reaction of chlorophosphines 3 with the silver diazo compounds 4 - undergo spontaneous dimerization accompanied by a P » P O-shift to yield the λ5-diphosphetes 9 . Their structural assignment is based on an X-ray crystal structure analysis of 9a as well as on ring cleavage by water ( 9 » 10 ).

Cycloaddition of N-acylimines with cyclobutadienes

Abstract N-Acylimines (2) possess the characteristics of both hetero-1,3-dienes and dienophiles. They react with the kinetically stabilised cyclobutadienes 1 to form 4-aza-2-oxabicyclo[4.2.0]octa-3,7-dienes (3) and/or 2-azabicyclo[2.2.0]hex-5-enes (4). Compounds of the type 3 undergo acid-catalysed isomerisation to give compounds 4. Homocyclopropenylium intermediates of the type 5 are supposed to be involved in both processes (1 + 2 → 3 + 4 and 3 → 4).