A Highly Diastereoselective Pinacol Coupling Reaction of Aldehydes and Ketones Using Low-Valence Niobium Generated from Nb(V)
作者:Shigeru Arai、Yukinori Sudo、Atsushi Nishida
DOI:10.1248/cpb.52.287
日期:——
racemic 1,2-diol mediated by low-valence niobium generated in situ is described. A 1,4-dioxane-toluene solvent system was found to be essential to achieve higher selectivities and to prevent other reactions of pinacols, such as deoxygenation and acetal formation. Aromatic aldehydes and ketones were converted to the corresponding pinacols with up to 97 and 85% de, respectively.
Treatment of aromatic carbonyl compounds with Zn powder in 10% aq NaOH solution without using any organic solvents under the mild conditions afforded the corresponding 1,2-diols in good yields.
of manganese as a mediator for allylations and pinacol couplings in aqueousmedia was investigated. The combination of manganese and copper is found to be a highly effective mediator for the allylation of aryl aldehydes in water. Such a combination is found to be more reactive than other previously reported metals in aqueousmedia. No reaction was observed with either manganese or copper alone as the
Stereoselective Barbier-Type Allylations and Propargylations Mediated by CpTiCl<sub>3</sub>
作者:Josefa L. López-Martínez、Irene Torres-García、Ignacio Rodríguez-García、Manuel Muñoz-Dorado、Miriam Álvarez-Corral
DOI:10.1021/acs.joc.8b02643
日期:2019.1.18
CpTiCl2, prepared in situ by manganese reduction of CpTiCl3, is an excellent new system for the Barbier-typeallylation and propargylation of carbonyl compounds. It can be used in catalytic amounts when combined with Et3N·HBr/TMSBr, which acts as a regenerating system. The high regio- and stereoselectivity shown by this system makes it useful for prenylation and crotylation processes in the synthesis