Enantioselective rhodium-catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and terminal alkynes: application to the total synthesis of (+)-lasubine II.
The use of TADDOL-based phosphoramidite ligands on rhodium allows for the incorporation of terminal alkynes in the [2+2+2] cycloaddition with alkenyl isocyanates. Terminal aliphatic alkynes provide bicyclic lactams, while the use of aryl alkynes provides complementary access to vinylogous amides. Product selectivity seems to be governed by a combination of electronics and sterics, with smaller and/or more electron-deficient substituents favoring lactam formation. The use of homologous alkenyl isocyanates leads to an expedient asymmetric total synthesis of the alkaloid lasubine II.
Yu
Robert T
RT
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
Rovis
Tomislav
T
D000475:Alkenes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D017953:Isocyanates / Q000737:chemistry*; D011807:Quinolizines / Q000138:chemical synthesis* / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry; D013237:Stereoisomerism
D000475:Alkenes; D000480:Alkynes; D017953:Isocyanates; D011807:Quinolizines; C414385:lasubin I; D012238:Rhodium