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An Overlooked Pathway in 1,3-Dipolar Cycloadditions of Diazoalkanes with Enamines.

ABSTRACT: Methyl diazoacetate reacts with 1-(N-pyrrolidino)cycloalkenes to give products of 1,3-dipolar cycloadditions and azo couplings. The kinetics and mechanisms of these reactions were investigated by NMR spectroscopy and DFT calculations. Orthogonal π-systems in the 1,3-dipoles of the propargyl-allenyl type allow for two separate reaction pathways for the (3+2)-cycloadditions. The commonly considered concerted pathway is rationalized by the interaction of the enamine HOMO with LUMO+1, the lowest unoccupied orbital of the heteropropargyl anion fragment of methyl diazoacetate. We show that HOMO/LUMO(π*_N=N ) interactions between enamines and methyl diazoacetate open a previously unrecognized reaction path for stepwise cycloadditions through zwitterionic intermediates with barriers approximately 40 kJ mol^-1 lower in energy in CHCl₃ (DFT calculations) than for the concerted path.

SUBMITTER: Li L

PROVIDER: S-EPMC9306659 | biostudies-literature |

REPOSITORIES: biostudies-literature

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