Acta Phys. -Chim. Sin. ›› 1996, Vol. 12 ›› Issue (06): 496-501.doi: 10.3866/PKU.WHXB19960604

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Theoretical Study on the Mechanism of the Cycloaddition Reactions Between Methyleneketene and 5-methylene-1,3-dioxan-4,6-dione

Sheng Ying-Hong,Fang De-Cai,Fu Xiao-Yuan   

  1. Department of Chemistry,Beijing Normal University,Beijing 100875
  • Received:1995-10-04 Revised:1996-01-29 Published:1996-06-15
  • Contact: Fu Xiao-Yuan

Abstract:

Three different reaction schemes for the cycloaddition reactions between methyleneketene and 5-methylene-1,3-dioxan-4,6-dione have been studied by means of semiempirical AM1 method. All the geometries of the stationary points on the reactions path have been optimized by energy gradient technique, and all transition states were characterized by vibration frequency analysis. The results can be summed up as follows: the cycloaddition of different double bond of methyleneketene with 5-methylene- 1,3-dioxan-4,6-dione are all concerted but nonsynchrorous, taking place through twisted transition states. An analysis based on frontier molecular orbital theory shows that the reaction mechanisms correspond to [4+2] description. The activation barriers were calculated to be 24.07k J •mol- 1, 32.41 k J•mol-1 and 137.96 kJ•mol- 1 respectively. The regio-selectivity of the reactions observed by experiments was correctly predicted by the calculations.

Key words: Methyleneketene, 5-methylene-1,3-dioxan-4,6-dione, Cycloaddition, Region-selectivity, Reaction mechanism