Control of four stereocentres in a triple cascade organocatalytic reaction

Intermolecular Cross-Double-Michael Addition between Nitro and Carbonyl Activated Olefins as a New Approach in C−C Bond Formation

A novel intermolecular cross-double-Michael addition between nitro and carbonyl activated olefins has been developed through Lewis base catalysis. The reaction took place with a large group of beta-alkyl nitroalkenes and alpha,beta-unsaturated ketone/esters, producing an allylic nitro compound in good to excellent yields.

Insights on co-catalyst-promoted enamine formation between dimethylamine and propanal through ab initio and density functional theory study

The mechanistic details on enamine formation between dimethylamine and propanal are unraveled using the ab initio and density functional theory methods. The addition of secondary amine to the electrophile and simultaneous proton transfer results in a carbinolamine intermediate, which subsequently undergoes dehydration to form enamine. The direct addition of amine as well as the dehydration of the resulting carbinolamine intermediate is predicted to possess fairly high activation barrier implying that a unimolecular process is unlikely to be responsible for enamine formation. Different models are therefore proposed which could explain the relative ease of enamine formation under neat condition as well as under the influence of methanol as the co-catalyst. The explicit inclusion of either the reagent or the co-catalyst is considered in the transition states as stabilizing agents. The participation of the reagent or the co-catalyst as a monofunctional ancillary species is found to stabilize the transition states relative to the unassisted or the direct addition/dehydration pathways. The reduction in enthalpy of activation is found to be much more dramatic when two co-catalysts participate in an active bifunctional mode in the rate-determining dehydration step. The transition structures exhibited characteristic features of a relay proton transfer mechanism. The free energy of activation associated with the two methanol-assisted pathway is found to be 16.7 kcal/mol lower than that of the unassisted pathway. The results are found to be in concurrence with the available reports on the rate acceleration by co-catalysts in the Michael reaction between enamine and methyl vinyl ketone under neat conditions.

Enantioselective formal [3+3] annulation for the direct construction of bicyclic skeletons with four stereogenic centers

An enantioselective formal [3+3] annulation reaction of cyclic ketones with enones has been developed. In the presence of 20 mol % of pyrrolidine-thiourea 1a or N-(pyrrolidin-2-ylmethyl)trifluoromethanesulfonamide 1i, the reactions afford bicyclo [3.3.1] adducts in moderate to good yields with good to high enantioselectivities under mild conditions.

Highly selective cascade couplings for the syntheses of functionalized piperidinones and bispidines

Efficient cascade couplings to synthesize functionalized piperidinones 1 and bispidines 2 and 3 have been developed. Simple modifications to the reaction conditions allow for the highly controlled and selective formation of each compound. In addition, the cis isomer of 1 can be selectively obtained under acidic conditions, while the preparation of the corresponding trans isomer can also be readily realized through a base-catalyzed, dynamic crystallization-driven process.

Bimorpholine-Mediated Enantioselective Intramolecular and Intermolecular Aldol Condensation

Monosalts of N-substituted bimorpholine derivatives are efficient organocatalysts in intramolecular and intermolecular aldol reactions. The properties of the catalysts can be tuned either by the selection of an appropriate acid for the salt formation or by the change of a substituent at the nitrogen atom. In aldol condensation, i-Pr-substituted bimorpholine is the most stereoselective catalyst affording products in high yield with enantioselectivities up to 95% ee.

Enantioselective Organocatalytic Double Michael Addition Reactions

[reaction: see text] A novel organocatalytic, enantioselective domino double Michael addition reaction of alpha,beta-unsaturated aldehydes with ethyl 4-mercapto-2-butenoate has been developed. The process is promoted by chiral diphenylprolinol TMS ether to give chiral tetrahydrothiophenes in high to excellent levels of enantioselectivities.

Asymmetric Organocatalytic Domino Reactions

The current status of organic synthesis is hampered by costly protecting-group strategies and lengthy purification procedures after each synthetic step. To circumvent these problems, the synthetic potential of multicomponent domino reactions has been utilized for the efficient and stereoselective construction of complex molecules from simple precursors in a single process. In particular, domino reactions mediated by organocatalysts are in a way biomimetic, as this principle is used very efficiently in the biosynthesis of complex natural products starting from simple precursors. In this Minireview, we discuss the current development of this fast-growing field.