Rhodium-catalyzed oxygenative [2 + 2] cycloaddition of terminal alkynes and imines for the synthesis of β-lactams.
A rhodium-catalyzed oxygenative [2 + 2] cycloaddition of terminal alkynes and imines has been developed, which gives β-lactams as products with high trans diastereoselectivity. In the presence of a Rh(I) catalyst and 4-picoline N-oxide, a terminal alkyne is converted to a rhodium ketene species via oxidation of a vinylidene complex and subsequently undergoes a [2 + 2] cycloaddition with an imine to give rise to the 2-azetidinone ring system. Mechanistic studies suggest that the reaction proceeds through a metalloketene rather than free ketene intermediate. The new method taking advantage of catalytic generation of a ketene species directly from a terminal alkyne provides a novel and efficient entry to the Staudinger synthesis of β-lactams under mild conditions.
Department of Chemistry, Seoul National University , Seoul 151-747, Republic of Korea.
Insu
I
Kim
Sang Weon
SW
Roh
Dong Gil
DG
Lee
Chulbom
C
Lee
D000480:Alkynes / Q000737:chemistry*; D001384:Azetidines / Q000737:chemistry*; D002384:Catalysis; D003497:Cyclic N-Oxides / Q000138:chemical synthesis* / Q000737:chemistry; D061565:Cycloaddition Reaction; D007097:Imines / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism; D047090:beta-Lactams / Q000138:chemical synthesis* / Q000737:chemistry
C116379:2-azetidinone; D000480:Alkynes; D001384:Azetidines; D003497:Cyclic N-Oxides; D007097:Imines; D047090:beta-Lactams; D012238:Rhodium