The synthesis of a second-generation cobalt catalyst for the formation of trans-THF products via the Mukaiyama aerobic oxidative cyclization is reported. Two procedures have been developed with the new water-soluble catalyst that give superior yields and greatly simplify purification compared to the previous catalysts.
Abstract:The annulation reaction between various indoles and 2-alkoxycyclopropanoate esters is reported. Both high efficiency and complete stereochemical control was observed in some cases with this annulation process. A single stereocenter on the cyclopropane controls the diastereoselective formation of up to four new stereocenters. A different reaction course was observed with 3-substituted indole substrates, and an intervening C-3 to C-2-migration process arose that gives synthetically useful C-2 alkylation indole products.
The formal [3+2] dipolar cycloaddition (or annulation) of donor‐acceptor cyclopropanoate esters with pyridines and 5‐nitroquinoline is reported. Electron‐deficient pyridine dipolarophiles (R=CN, CO2Et, COMe) participate in the annulation whereas electron rich species do not. The product 2,3‐dihydroindolizines undergo rapid autooxidation, and the X‐ray structures for two of the aromatic products are reported.
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