A theoretical study of the cycloaddition between cyclopentadiene and allylideneammonium cation: an AM1 study

Pyrrolidine catalyzed reactions of cyclopentadiene with α,β-unsaturated carbonyl compounds: 1,2- versus 1,4-additions

A systematic study of the reactions of cyclopentadiene with α,β-unsaturated carbonyl compounds in the presence of catalytic pyrrolidine-H₂O revealed that the reactions can either proceed with a Michael attack at the β-carbon of enone, or 1,2-addition to the carbonyl, leadingeither to 4-cyclopentadienyl-2-butanones or 6-vinylfulvenes. The former can be isolated and/or converted to the corresponding 1,2-dihydropentalenes with base (or in one-pot at longer reaction times). Substitution pattern on the enones on the competing pathways have been studied and consistent mechanisms are proposed.

Secondary and primary amine catalysts for iminium catalysis

Formation of iminium ions from the condensation of chiral secondary or primary amines with alpha,beta-unsaturated aldehydes or ketones can be used as an effective platform for the acceleration of a wide variety of catalytic asymmetric cycloaddition and conjugate addition reactions. The reversible formation of the active iminium ion species simulates the pi-electronics and equilibrium dynamics traditionally associated with Lewis acid activation of alpha,beta-unsaturated carbonyl compounds lowering the energy level of the LUMO associated with the pi-system and activating subsequent reaction. Importantly, these iminium ion catalysed processes offer the opportunity to conduct reactions in the presence of both moisture and air greatly adding to the practicality and general applicability of the chemistry described. Proposed catalytic cycles and transition state models for the induction of asymmetry provide reliable and robust predictive tools for the outcome of reactions and high functional group tolerance suggests this class of transformation will have broad application in the arena of synthetic organic chemistry as the area matures. This review describes the rapid expansion of iminium ion catalysis over recent years from its conceptual introduction to the development of a whole new arsenal of highly practical and effective methods with which to approach challenging and fundamental bond construction processes.

Origins of stereoselectivity in Diels-Alder cycloadditions catalyzed by chiral imidazolidinones

B3LYP/6-31G(d) density functional theory has been used to study Diels-Alder reactions of cyclopentadiene with alpha,beta-unsaturated aldehydes and ketones organocatalyzed by MacMillan's chiral imidazolidinones. Preferred conformations of transition structures and reaction intermediates have been located. The dramatically different reactivities and enantioselectivities exhibited by two similar chiral imidazolidinones are rationalized.