Seven structurally distinct pentadienyl type lithium and potassium compounds were screened against a variety of electrophiles in order to assess the regioselectivity of the trapping reactions. Organoborates and analogs thereof (fluorodimethoxyborane) proved to be perfectly regioreliable attacking only unsubstituted terminal positions and thus providing, after oxidation, exclusively primary allylic alcohols. 2,4-Pentadienyllithiums or -potassiums, that carry a methyl group at the 1- or 3-position, exhibit the same extreme regioselectivity towards halotrialkylsilanes or carbon dioxide. Although the unsubstituted parent compounds combine with such electrophiles still preferentially at the terminal position, considerable proportions of branched products are concomitantly formed as well (1/3-attack ratios ranging from 2:1 to > 20:1). Hydroxyalkylating and alkylating reagents such as formaldehyde, oxirane or butyl iodide invariably afford regioisomeric mixtures generally varying in composition between 3:1 and 1:3. The condensation reaction with halotrialkylsilanes appears to follow a concerted (SN2-like) rather than an addition/elimination (ate complex-mediated) mechanism.
Hydroformylation of 1,4-diolefins in the presence of primary amines leading to heterocyclic compounds
作者:Christian L. Kranemann、Beate E. Kitsos-Rzychon、Peter Eilbracht
DOI:10.1016/s0040-4020(99)00162-3
日期:1999.4
The Rh(I)-catalysed hydroformylation of dienes in the presence of amines is applied to heterocyclic ring synthesis. Starting from 1,4-dienes pyrroles or eight-memberedheterocycles are easily accessible. The selectivity of the reaction is controlled by the substitution pattern of the diolefin.