Zu-Feng Xiao

Ruthenium-catalyzed asymmetric N-demethylative rearrangement of isoxazolidines and its application in the asymmetric total syntheses of (-)-(1R,3S)-HPA-12 and (+)-(1S,3R)-HPA-12.

An asymmetric N-demethylative rearrangement of 1,2-isoxazolidines catalyzed by ruthenium is described. Enantioenriched syn-1,3-aminoalcohols as well as cis-1,3-oxazinanes, which are useful building blocks, can be efficiently prepared stereospecifically by this reaction in good yields, via the isoxazolidine intermediates in situ generated from a nitrone bearing a chiral auxiliary and styrenes. This asymmetric reaction was also applied in the asymmetric total syntheses of both (-)-(1R,3S)-HPA-12 and (+)-(1S,3R)-HPA-12.

Synthesis of syn-1,3-Aminoalcohols via a Ru-Catalyzed N-Demethylative Rearrangement of Isoxazolidines and Its Application in a Three-Step Total Synthesis of HPA-12

A highly efficient ruthenium-catalyzed stereospecific N-demethylative rearrangement of isoxazolidines to synthetically useful N-H-1,3-oxazinanes is described. 1,3-Oxazinanes are useful building blocks, which can be further converted to N-H-1,3-aminoalcohols in one step. This new method was used in a three-step gram-scale total synthesis of HPA-12 in an overall 24% yield.

Ru-catalyzed rearrangement of N-methyl isoxazolidines to N-H 1,3-oxazinanes: a strategy of self-hydride transferring cleavage of N-O bonds.

A strategy of ruthenium-catalyzed self-hydride transferring cleavage of N-O bonds was designed and utilized in a cascade 1,3-dipolar cyclization of alkenes and N-methyl nitrones followed by an N-demethylative rearrangement, furnishing synthetically useful N-H 1,3-oxazinanes.

Transition-Metal-Free Self-Hydrogen-Transferring Allylic Isomerization

Phenanthroline and tert-butoxide have been established as powerful radical initiators in reactions such as the SRN1-type coupling reactions due to the cooperation of large heteroarenes and a special feature of tert-butoxide. The first phenanthroline-tert-butoxide-catalyzed transition-metal-free allylic isomerization is described. The resulting ketones are key intermediates for indenes. The control experiments rule out the base-promoted allylic anion pathway. The radical pathway is supported by experimental evidence that includes kinetic study, kinetic isotope effect, isotope-labeling experiments, trapping experiments, and EPR experiments.

Synthesis of Highly Functionalized Indoles and Indolones via Selectivity-Switchable Olefinations

Highly functionalized indoles and indolones were prepared via selectivity-switchable mono- or diolefinations. The Julia olefination of the products followed by a Brønsted acid-prompted cyclization afforded indolones, whereas the indoles were obtained by a sequential Wittig olefination and electrocyclization. This method opens divergent access to highly functionalized nitrogen-containing bicyclic or tricyclic heterocycles.