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.

Iridium-Catalyzed Cyclization of Isoxazolines and Alkenes: Divergent Access to Pyrrolidines, Pyrroles, and Carbazoles.

A heterogeneous iridium-complex-catalyzed N-O-cleaving rearrangement/cyclization of 2,3-dihydroisoxazoles with alkenes has been developed. It provides divergent access to multiple substituted pyrrolidines, pyrroles, and carbazoles. The iridium catalyst remains highly catalytic active after seven cycles. The gram-scale synthesis afforded a carbazole with strong bluish-violet fluorescence.

Transition-metal-free oxychlorination of alkenyl oximes: in situ generated radicals with tert-butyl nitrite.

Oxychlorination of alkenyl oximes is harder compared to the analogous oxybromination or oxyiodination because of the difficulty associated with the formation of chlorine cations or radicals. A transition-metal-free oxychlorination of alkenyl oximes has been developed, using t-BuONO as a dual oxidant and AlCl3 as a chlorine source. This convenient and practical method has been used to construct chloroisoxazolines in moderate to good yields, whereas N-chlorosuccinimide (NCS) failed to promote this reaction.

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.

Direct Alkylation of Amines with Alcohols Catalyzed by Base.

A base-catalyzed/promoted transition-metal-free direct alkylation of amines with alcohols has been developed, giving the desired amines in generally high yields from either aromatic or aliphatic alcohols. On the basis of the (1)H NMR and in situ IR (React-IR) monitoring experiments, isotope-labeling experiments, as well as control experiments, a novel "hemiaminal" model is proposed to understand the mechanism, which explains the formation of the "extra" aldehyde in the reaction.

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.