During an alkyne-carbonyl metathesis reaction between electron-rich 3-arylprop-2-inylcarboxylates and electron-poor benzaldehydes, a smooth migration of carboxylate groups takes place. This unique cascade reaction allows the formation of Morita-Baylis-Hillman (MBH) adducts unavailable via a traditional MBH reaction.

Catalyst-free addition of ketone enolate to nonactivated multiple CÀCb onds involves non-complementary reaction partners and typically requires super-basic conditions. On the other hand, highly aggregated or solvated enolates are not reactive enough to undergo direct addition to alkenes or alkynes.Herein, we report an ew anionic cascade reaction for one-step assembly of intriguing molecular scaffolds possessing contiguous six-, five-, and four-membered rings,r epresenting af ormal [2+ +2] enol-allene cycloaddition. Reaction proceeds under very mild conditions and with excellent diastereoselectivity.D eeper mechanistic and computational studies revealed unusually slow proton transfer phenomenon in cyclic ketone intermediate and explained peculiar stereochemical outcome.

No abstract

No abstract

Mechanistic studies of the reaction between 3-arylprop-2-ynyl esters and aldehydes catalyzed by BF3 ⋅Et2 O were performed by isotopic labeling experiments and quantum chemical calculations. The reactions are shown to proceed by either a classical alkyne-carbonyl metathesis route or an unprecedented addition-rearrangement cascade. Depending on the structure of the starting materials and the reaction conditions, the products of these reactions can be Morita-Baylis-Hillman (MBH) adducts that are unavailable by traditional MBH reactions or E- and Z-α,β-unsaturated ketones. (18) O-Labeling studies suggested the existence of two different reaction pathways to the products. These pathways were further examined by quantum chemical calculations that employed the DFT(wB97XD)/6-311+G(2d,p) method, together with the conductor-like screening model for realistic solvation (COSMO-RS). By using the wB97XD functional, the accuracy of the computed data is estimated to be 1-2 kcal mol(-1) , shown by the careful benchmarking of various DFT functionals against coupled cluster calculations at the CCSD(T)/aug-cc-pVTZ level of theory. Indeed, most of the experimental data were reproduced and explained by theory and it was convincingly shown that the branching point between the two distinct mechanisms is the formation of the first intermediate on the reaction pathway: either the four-membered oxete or the six-membered zwitterion. The deep mechanistic understanding of these reactions opens new synthetic avenues to chemically and biologically important α,β-unsaturated ketones.