Synthesis 2001(12): 1830-1836
DOI: 10.1055/s-2001-17521
PAPER
© Georg Thieme Verlag Stuttgart · New York

Pentadienyl Type Lithium and Potassium Species: The Regioselectivity of their Reactions with Electrophiles

Manfred Schlosser*, Armin Zellner, Frédéric Leroux
Section de Chimie, Université, BCh, 1015 Lausanne, Switzerland
Fax: +41(21)6923965; e-Mail: manfred.schlosser@ico.unil.ch;
Further Information

Publication History

Received 9 April 2001
Publication Date:
11 August 2004 (online)

Abstract

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.

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Rauchschwalbe, G.; Schlosser, M.; unpublished results, 1976.