Cobalt(II)-catalyzed 1,4-addition of organoboronic acids to activated alkenes: an application to highly cis-stereoselective synthesis of aminoindane carboxylic acid derivatives.

It all adds up: The 1,4-addition of organoboronic acids to activated alkenes catalyzed by [Co(dppe)Cl(2)] is described. A [3+2]-annulation reaction of ortho-iminoarylboronic acids with acrylates to give various aminoindane carboxylic acid derivatives with cis-stereoselectivity is also demonstrated (see scheme; dppe = 1,2-bis(diphenylphosphino)ethane).

Nickel-catalyzed Mizoroki-Heck- versus Michael-type addition of organoboronic acids to alpha,beta-unsaturated alkenes through fine-tuning of ligands.

Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br2], ZnCl2, and H2O in CH3CN at 80 degrees C to give the corresponding Mizoroki-Heck-type addition products in good to excellent yields. Furthermore, 1 equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael-type addition was achieved in a very selective manner. Thus, various p- and o-substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH3CN at 80 degrees C for 12 h catalyzed by Ni(acac)2, P(o-anisyl)3, and K2CO3 to give the corresponding Michael-type addition products in excellent yields. However, for m-substituted arylboronic acids, the yields of Michael-type addition products are very low. The cause of this unusual meta-substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m-substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki-Heck-type products and dry reaction conditions for Michael-type addition products. Possible mechanistic pathways for both addition reactions are proposed.

Cobalt-catalyzed highly regio- and stereoselective intermolecular reductive coupling of alkynes with conjugated alkenes.

In the presence of Co(PPh3)2I2, PPh3, water, and zinc powder, the reaction of alkynes (R1CCR2: R1 = Ph, R2 = Me (1a); R1 = Ph, R2 = Ph (1b); R1 = Et, R2 = Et (1c); R1 = Ph, R2 = (CH2)3OH (1d); R1 = CO2Et, R2 = Ph (1e); R1 = CO2Me, R2 = (CH2)4CH3 (1f); R1 = CO2Et, R2 = SiMe3 (1g)) with alkenes having an electron-withdrawing substituent (CH2=CHR: R = CO2Bu (2a), CN (2b), SO2Ph (2c) and CO2Me (2d)) proceeded smoothly in acetonitrile to give the corresponding reductive coupling products (R1HC=CR2CH2CH2R, 3a-j) in fair to excellent yields. This reductive coupling is highly regio- and stereoselective; only one isomer was observed for each reaction. The results of an isotope-labeling experiment using D2O (99%) to replace normal water for the reductive coupling of vinyl phenyl sulfone 2c with alkyne 1a revealed that the product is E-Ph(D)C=CMeCH2CH(D)SO2Ph deuterated at the olefinic proton and one of the protons of the alpha-methylene group in 84 and 96%, respectively. Possible mechanisms for this highly regio- and stereoselective ene-yne catalytic reaction are proposed.