Iodine monobromide (IBr) at low temperature: enhanced diastereoselectivity in electrophilic cyclizations of homoallylic carbonates
摘要:
Iodine monobromide affords superior diastereoselectivity in low-temperature electrophilic cyclizations of homoallylic carbonates. Solvent and temperature effects and the scope and limitations of the method are discussed; optimal selectivity is obtained in toluene at -80 to -85-degrees-C. The latter protocol generally furnishes significantly enhanced selectivity, vis-a-vis the original procedure employing 12 in acetonitrile at -20-degrees-C; for example, the IBr-induced cyclization of 14 affords a 25.8:1 mixture of 15 and 16, whereas I2 gives an 8.4:1 ratio. An equilibration experiment established that the diastereoselectivity derives primarily or exclusively from kinetic control of the cyclization process.
A Joint Experimental-Computational Comparative Study of the Pd<sup>0</sup>-Catalysed Reactions of Aryl Iodides and Aldehydes with N, O, and S Tethers
作者:Daniel Solé、Francesco Mariani、Israel Fernández
DOI:10.1002/ejoc.201500393
日期:2015.6
heteroatom (nitrogen, oxygen, and sulfur) on the course of the palladium-catalysed intramolecular reactions of aryliodides and aldehydes having heteroatom-containing tethers has been explored by an extensive experimental–computational (DFT) study. Two series of substrates were considered, namely aldehydes bearing either the α-(2-iodobenzylheteroatom) or β-(2-iodophenylheteroatom) moieties. While some
Synthetic studies on bryostatins, potent antineoplastic agents: Synthesis of the C17C27 fragment of C20 oxygenated bryostatins
作者:Ken Ohmori、Shigeru Nishiyama、Shosuke Yamamura
DOI:10.1016/0040-4039(95)01310-e
日期:1995.9
Synthetic process towards the bottom half portion of C20 oxygenated series of bryostatins is described. The stereogenic center at C20 position was constructed through a hydroxyl group-directed epoxidation by using mCPBA. It was found that silver (I) salt is an effective and mild reagent for regioselective ring cleavage of α-bromoepoxides into the corresponding α-hydroxyketones via oxonium ion intermediates