Abstract
The allenecarboxylates 1a, b and allenic lactones 4a, b undergo thermally induced (1,3) H shifts in the presence of Co2(CO)8. The non-isolated 1,3-dienes 2a,b react further affording the Diels-Alder adducts 3a, b (Scheme 1) in high yields. These adducts were not formed in the case of the 2-vinylbutenolides 5a, b (Scheme 2). On irradiation in the presence of Co2(CO)8 or Mn2(CO)10, the studied allenes reacted in a different manner, yielding either cyclization products 7 and 8 (Scheme 3) or products 9 and 10, formed via H abstraction and solvent addition (Schemes 4 and 5).
Trifonov, Latchezar S