Phosphine-catalyzed cycloadditions of allenic ketones: new substrates for nucleophilic catalysis.
A range of phosphine-catalyzed cycloaddition reactions of allenic ketones have been studied, extending the scope of these processes from the more widely used 2,3-butadienoates to allow access to a number of synthetically useful products. Reaction of allenyl methyl ketone 4 with exo-enones afforded spirocyclic compounds in good regioselectivity and promising enantioselectivity via a [2 + 3] cycloaddtion. Aromatic allenyl ketones undergo a phosphine-promoted dimerization to afford functionalized pyrans, leading to a formal [2 + 4] Diels-Alder product, but did not react in the [2 + 3] cycloaddition. The results from other reactions that had found utility with 2,3-butadienoates are also reported.
Wallace
Debra J
DJ
Department of Process Research, Merck Sharp and Dohme Research Laboratories, Hertford Road, Hoddesdon, Herts, EN11 9BU, UK. debra_wallace@merck.com
Sidda
Rachel L
RL
Reamer
Robert A
RA
D000466:Alkadienes / Q000138:chemical synthesis*; D002070:Butadienes / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D007659:Ketones / Q000138:chemical synthesis*; D008956:Models, Chemical; D010720:Phosphines / Q000737:chemistry*
D000466:Alkadienes; D002070:Butadienes; D007659:Ketones; D010720:Phosphines; C025947:propadiene; C044646:phosphine