Synthetic Approaches to Phosphasugars (2-oxo-1,2-oxaphosphacyclanes) Using the Anomeric Alkoxyl Radical ß-Fragmentation Reaction as the Key Step.

The anomeric alkoxyl radical ß-fragmentation (ARF) of carbohydrates possessing an electron-withdrawing group (EWG) at C2, promoted by PhI(OAc)2/I2, gives rise to an acyclic iodide through which a pentavalent atom of phosphorus can be introduced via the Arbuzov reaction. After selective hydrolysis and subsequent cyclization, the phosphonate or phosphinate intermediates can be converted into 2-deoxy-1-phosphahexopyranose and 2-deoxy-1-phosphapentopyranose sugars. The ARF of carbohydrates with an electron-donor group (EDG) at C2 proceeds by a radical-polar crossover mechanism, and the cyclization occurs by nucleophilic attack of a conveniently positioned phosphonate or phosphinate group to the transient oxocarbenium ion. This alternative methodology leads to 5-phosphasugars with a 4-deoxy-5-phosphapentopyranose framework. The structure and conformation of the 2-oxo-1,2-oxaphosphinane and 2-oxo-1,2-oxaphospholane ring systems in different carbohydrate models have been studied by NMR and X-ray crystallography.

Photochemical C-H Amination of Ethers and Geminal Difunctionalization Reactions in One Pot.

A mild, atom-economic, and metal-free α-C-H amination of ethers using relatively stable nonafluorobutanesulfonyl (nonaflyl, Nf) azide as the aminating reagent to give N-sulfonyl hemiaminals is reported. This enables unprecedented C(sp3 ) difunctionalization reactions, leading to diverse functionalized amino group containing compounds starting from simple ethers in one pot.

Synthesis of chiral ß-iodo- and vinylorganophosphorus(V) compounds by fragmentation of carbohydrate anomeric alkoxyl radicals.

A new general methodology for the synthesis of chiral vinylphosphonate and vinylphosphine oxide carbohydrate derivatives has been developed using the anomeric alkoxyl radical fragmentation reaction as the key step. The synthetic sequence proceeded via ß-iodophosphonate and ß-iodophosphine oxide intermediates, which may be interesting synthons for the introduction of phosphorus into organic molecules. These vinylphosphonates could be easily transformed into 2-methylene-1-phosphapentofuranoses (3-methylene-1,2-oxaphospholanes) and ß-aminophosphonates, isosteres of biologically active α-methylene-γ-lactones and ß-amino acids, respectively.