Sherman J.L. Lauw

Brønsted Acid-Catalyzed Cycloisomerization of But-2-yne-1,4-diols with or without 1,3-Dicarbonyl Compounds to Tri- and Tetrasubstituted Furans

A Brønsted acid-catalyzed method to prepare tri- and tetrasubstituted furans efficiently from cycloisomerization of but-2-yne-1,4-diols with or without 1,3-dicarbonyl compounds is described. By taking advantage of the orthogonal modes of reactivity of the alcoholic substrate through slight modification of the reaction conditions, a divergence in product selectivity was observed. At room temperature, p-TsOH·H(2)O-mediated tandem alkylation/cycloisomerization of the propargylic 1,4-diol with the β-dicarbonyl compound was found to selectively occur to provide the tetrasubstituted furan product. On the other hand, increasing the reaction temperature to 80 °C was discovered to result in preferential p-TsOH·H(2)O-catalyzed dehydrative rearrangement of the unsaturated alcohol and formation of the 2,3,5-trisubstituted furan adduct.

Sulfoxidation of alkenes and alkynes with NFSI as a radical initiator and selective oxidant

Sulfoxides are important functional molecules. We develop a short-route (one-pot) synthesis of this class of molecules by reacting thiols with alkenes or alkynes under mild and metal-free conditions. N-Fluorobenzenesulfonimide (NFSI) is used to play dual roles: as a radical initiator for a thiol-ene/-yne reaction to form sulfide adducts, and as efficient oxidant for conversion of the sulfides formed in situ to sulfoxides. Over-oxidation of the sulfoxides to sulfones is avoided in our approach.

Electrochemical proton reduction catalysed by selenolato-manganese carbonyl complexes

Four manganese selenolato carbonyl complexes [Mn(CO)4(μ-SePh)]2 1, Mn2(CO)4(μ-CO)(μ-SePh)2(PBu3)2 (2, PBu3 = tri-n-butylphosphine), Mn(CO)4(μ-SePh)2Mn(CO)3(Py)(3, Py = pyridine) and Mn(CO)3(SePh)(DPPP) (4, DPPP = 1,3-bis(diphenylphosphino)propane) have been synthesized and structurally characterized by X-ray crystallography. Their electrocatalytic proton reduction properties have been measured with cyclic voltammetry in dichloromethane using CF3COOH as the proton source. Overpotentials ranging from 0.79 V to 0.89 V were determined for these complexes. The presence of different ligands such as phosphine and pyridine only made moderate differences to the overpotential and efficiency of the proton reduction process. The first step in the proton reduction pathway occurs via electroreduction of the Mn complexes based on reactivity studies and cyclic voltammetry data.

Trimerization of enones under air enabled by NHC/NaOtBu via a SET radical pathway

An unusual trimerization of enone via a formal [2 + 2 + 2] process is disclosed. The reaction is initiated by a radical process enabled by NaOtBu and N-heterocyclic carbene (NHC). Molecular oxygen (air) is involved in key steps of the radical intermediate formation and carbon–carbon bond cleavage in this trimerization reaction to form highly substituted cyclohexane derivatives. In previous studies, alkali metal tert-butoxides such as NaOtBu were mainly employed to generate radical intermediates from aryl halides. Here we provide a new avenue in using NaOtBu and combined NHC/NaOtBu to generate radical intermediates from enones for further reactions.