title: Theoretical elucidation of the rhodium-catalyzed [4 + 2] annulation reactions.
abstract: The reaction mechanism of the Rh-catalyzed [4 + 2] annulation of 4-alkynals with isocyanates is unraveled using density functional calculations. The reaction mechanisms of the model system and the real substituted system have been investigated and the results are compared. From our theoretical results based on the model and real substituted system, it is shown that (a) the rate-determining step is the Rh-H addition to the alkyne, (b) the formation of the cyclopentenone G and glutarimide K represents a severe competition, and (c) the product selectivity should be controlled by the amount of the isocyanates. In addition, it is demonstrated that there exist steric effects in the real substituted system, but missed in model system. Our calculations also show that although the results obtained on the model system could explain the mechanism in principle, the real substituted system could reflect the mechanism more exactly and make the reaction proceed with regioselectivity.
authors.affiliation: State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China.
authors.forename: Cai-Yun
authors.initials: CY
authors.lastname: Geng
authors.forename: Ji-Lai
authors.initials: JL
authors.lastname: Li
authors.forename: Xu-Ri
authors.initials: XR
authors.lastname: Huang
authors.forename: Hui-Ling
authors.initials: HL
authors.lastname: Liu
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Li
authors.forename: Chia-Chung
authors.initials: CC
authors.lastname: Sun
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry; D002384:Catalysis; D003198:Computer Simulation; D003500:Cyclization; D003517:Cyclopentanes / Q000138:chemical synthesis / Q000737:chemistry; D017953:Isocyanates / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D015394:Molecular Structure; D010881:Piperidones / Q000138:chemical synthesis / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000447:Aldehydes; D000480:Alkynes; D003517:Cyclopentanes; D017953:Isocyanates; D008024:Ligands; D010881:Piperidones; D012238:Rhodium; C007864:glutarimide; C013905:cyclopentenone