Mechanistic Investigations on the Interaction of Morita-Baylis-Hillman Ketones with 2-Aminothiophenol.

The reaction of Morita-Baylis-Hillman ketones with 2-aminothiophenol mediated by Cs2CO3 results in an oxidative cyclization to 2,2-disubstituted dihydro-1,4-benzothiazines, with the structure of the product indicating the occurrence of an aza-Michael addition along the pathway. In contrast, in the absence of a base, the parent compounds interact to produce a thia-Michael adduct instead. A deeper mechanistic study improved our understanding of the apparent contradiction and provided insight into the base-dependent switch in reactivity.

Acyl Transfer-Driven Rauhut-Currier Dimerization of Morita-Baylis-Hillman Ketones.

A serendipitous Rauhut-Currier dimerization of 1,1-disubstituted activated olefins derived from Morita-Baylis-Hillman adducts was observed in the presence of DABCO. The reaction is driven by the migration of an acyl group and produces multifunctionalized enol esters in yields greater than 90% in most cases, without necessitating column chromatographic purification. The acyl transfer is thought to proceed via a transition state typical of a Morita-Baylis-Hillman (MBH) reaction, supported by a brief mechanistic study involving computational calculations.

Synthesis of 2,2-Disubstituted Dihydro-1,4-benzothiazines from Morita-Baylis-Hillman Ketones by an Oxidative Cyclization.

An oxidative cyclization ensued upon interaction of Morita-Baylis-Hillman (MBH) ketones with 2-aminothiophenol in the presence of Cs2CO3, resulting in the formation of new 2,2-disubstituted dihydro-1,4-benzothiazines. The reaction features an aza-Michael addition and an oxidative cyclization involving the formation of a carbon-sulfur bond and works well over a wide range of MBH ketones to deliver the dihydrobenzothiazines in good yields in reasonable reaction times under mild conditions.

Diamine-mediated degradative dimerisation of Morita-Baylis-Hillman ketones.

A degradative dimerisation of Morita-Baylis-Hillman ketones was observed in the presence of a primary diamine. The reaction proceeded swiftly to produce methylene-bridged 1,3-dicarbonyl compounds. A brief mechanistic investigation alluded to a retro-Mannich reaction as the key step of the transformation.

A Hydrazine Insertion Route to N'-Alkyl Benzohydrazides by an Unexpected Carbon-Carbon Bond Cleavage.

A serendipitous carbon-carbon bond cleavage in the reaction of benzoyl acrylates, derived from Morita-Baylis-Hillman adducts, with hydrazines delivered new N',N'-disubstituted benzohydrazides. The reaction features a regioselective formation of two carbon-nitrogen bonds and works well with a range of acrylates and hydrazines. A brief mechanistic investigation alluded to a cyclic hemiaminal as a plausible intermediate.

Probing the Synergistic Catalytic Model: A Rationally Designed Urea-Tagged Proline Catalyst for the Direct Asymmetric Aldol Reaction.

A urea tag was incorporated at the C-4 position of proline, cis to its COOH group, in order to explore the prospect of a synergistic effect between the two functional groups in the transition state of the enamine route to the asymmetric aldol reaction. The catalyst proved to be an excellent performer, delivering aldols in high yields and with excellent enantio- and diastereoselectivities using just 2 mol % loading in the presence of water; it also exhibited good levels of recyclability under aqueous conditions. The favorable results reveal the interesting possibility of an intramolecular host-guest interaction between the urea and the amino acid moieties, exerting a beneficial effect on catalysis. The concept could certainly offer a new direction toward more efficient catalyst design.

A modular approach to catalyst hydrophobicity for an asymmetric aldol reaction in a biphasic aqueous environment.

Catalyst 5, an ion pair consisting of a hydrophilic cation and a lipophilic anion, fulfils the solubility requirements needed to couple efficiency (enantioselectivities and anti-diastereoselectivities up to > or = 99%) and catalyst recyclability in asymmetric aldol reactions under aqueous biphasic conditions.