Synthetic Access to All Four Stereoisomers of Oxetin

Six-step total syntheses of (−)-galanthamine and (−)-

The Amaryllidaceae alkaloid (−)-galanthamine (1) is a reversible, competitive acetylcholinesterase inhibitor deployed clinically to treat the dementia associated with Alzheimer’s disease. Here, we describe a six-step synthesis of this natural product from simple, readily accessible starting materials. Enantioselective 1,2-reduction, Mitsunobu coupling, Heck cyclization and diastereoselective allylic oxidation reactions are used in our approach, which provides the shortest synthetic route to compound 1 reported to date. A simple modification to the closing stages of the sequence allows equally facile access to (−)-N-norgalanthamine (2), a compound with a range of distinctive biological properties. The concise and operationally simple synthetic protocols reported here could obviate the need to manipulate naturally sourced galanthamine in the pursuit of analogues required for pharmacological studies.

Formation of Tetrahydrothiophenes via a Thia-Paternò-Büchi-Initiated Domino Photochemical Reaction

We have established photochemical access to thietane or tetrahydrothiophene compounds from thiobenzophenone derivatives and acrylonitrile, wherein the product selectivity is controlled by a simple adjustment of the reagent concentration in solution. Small libraries of five-membered ring sulfur-containing compounds were prepared through a thia-Paternò-Büchi reaction, followed by a previously unknown regioselective photochemical ring enlargement reaction in a domino process or a stepwise fashion. A mechanism is proposed to rationalize this ring enlargement reaction via a carbene species provided from photoexcited thiocarbonyl compounds.

The Paternò–Büchi reaction – a comprehensive review

This review represents the most complete description of the scientific results obtained on a photochemical reaction described 110 years ago by an Italian scientist.

Total Synthesis of (-)-Mitrephorone A

The first synthesis of (-)-mitrephorone A is disclosed along with discussion and study of synthetic strategies. The natural product includes a highly congested hexacyclic ent-trachylobane diterpenoid framework featuring a rare, embedded oxetane. The synthetic analysis presented dissects a number of approaches for the synthesis of the central oxetane, including carbonyl-olefin photocycloadditions, Prins-type cyclizations, and oxidative ring closures. In the successful route, three [4 + 2] cycloadditions enable rapid construction of all carbocycles. A novel late-stage oxidative cyclization of a hydroxy diosphenol with Koser's reagent furnishes the pivotal oxetane moiety.

Cooperative 5- and 10-membered ring interactions in the 10-helix folding of oxetin homo-oligomers

Homo-oligomers of the natural product oxetin (cis-3-amino-2-oxetanecarboxylic acid) were prepared and their conformational behaviour studied in solution and solid state and by molecular modelling. The predominant secondary structure was a 10-helix, propiciously stabilized by a network of 5-membered ring H-bonds implicating ring oxygens and neighboring amide hydrogen atoms.

Studies on cyclization reactions of 3-amino-2,4-dihydroxybutanoic acid derivatives

Linear derivatives of the title compound are convenient precursors for regioselective cyclizations leading to highly-functionalized γ-lactones, oxazolidinones, oxazolines and aziridines.