Rh-catalyzed addition of arylboroxines to cyclic N-(isopropanesulfinyl)ketimines.

Arylboroxines, which are easily accessed by drying commercially available arylboronic acids, are added to N-(isopropanesulfinyl)ketimines derived from cyclohexanone, N-Boc-piperidin-4-one, and tetrahydropyran-4-one in high yields and with excellent functional group compatibility via rhodium catalysis. These results contrast with additions to the corresponding ketimines incorporating the larger N-tert-butanesulfinyl group, which give considerably lower yields. Efficient two-step preparation of racemic isopropanesulfinamide from inexpensive isopropyl disulfide and recycling of the isopropanesulfinyl group from the addition products are also described.

Highly functional group compatible Rh-catalyzed addition of arylboroxines to activated N-tert-butanesulfinyl ketimines.

The rhodium-catalyzed addition of readily accessible arylboroxines to N-tert-butanesulfinyl ketimines derived from oxetan-3-one, N-Boc-azetidin-3-one, and isatins proceeds in high yields with excellent functional group compatibility. Moreover, high diastereoselectivities are observed for the additions to the N-sulfinyl ketimines derived from isatins.

Mechanistic Analysis of Oxidative C-H Cleavages Using Inter- and Intramolecular Kinetic Isotope Effects.

A series of monodeuterated benzylic and allylic ethers were subjected to oxidative carbon-hydrogen bond cleavage to determine the impact of structural variation on intramolecular kinetic isotope effects in DDQ-mediated cyclization reactions. These values are compared to the corresponding intermolecular kinetic isotope effects that were accessed through subjecting mixtures of non-deuterated and dideuterated substrates to the reaction conditions. The results indicate that carbon-hydrogen bond cleavage is rate determining and that a radical cation is most likely a key intermediate in the reaction mechanism.

Gold-catalyzed synthesis of oxygen- and nitrogen-containing heterocycles from alkynyl ethers: application to the total synthesis of andrachcinidine.

In this paper we report that homopropargylic ethers containing pendent oxygen or nitrogen nucleophiles react with electrophilic gold catalysts in the presence of water to form saturated heterocyclic ketones. Mechanistic studies demonstrated that the reactions proceed through a sequence of alkyne hydration, alkoxy group elimination, and intramolecular conjugate addition. Diastereoselectivities for tetrahydropyran and piperidine formation are very good to excellent. This method has been applied to an efficient total synthesis of the natural product andrachcinidine. Utilizing propargylic ether substrates rather than homopropargylic ethers promotes regioselective hydration of internal alkynes, thereby expanding the scope of products that can be accessed through this protocol.

Gold-catalyzed heterocycle synthesis using homopropargylic ethers as latent electrophiles.

[reaction: see text] Homopropargylic ethers with pendent nucleophiles, when subjected to Au catalysts in aqueous solvent, provide heterocyclic ketones. The reactions are efficient, tolerant of functionality and ambient atmosphere, and operationally simple. Diastereoselectivity can be predicted on the basis of product thermodynamics. This process demonstrates the viability of homopropargylic ethers to serve as latent electrophiles that can be unraveled under highly selective conditions to promote heterocycle formation through nucleophilic additions to alpha,beta-unsaturated ketones.