β Scribed by Cai-Yun Geng; Ji-Lai Li; Xu-Ri Huang; Hui-Ling Liu; Zhuo Li; Chia-Chung Sun
No coin nor oath required. For personal study only.
The reaction mechanism of the Rhβcatalyzed [4 + 2] annulation of 4βalkynals 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 rateβdetermining step is the RhβH 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. Β© 2007 Wiley Periodicals, Inc. J Comput Chem, 2008
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