Abstract
The inexpensive room temperature ionic liquid (RTIL), [bmim][Br] has been found to be a superior medium for the Bi-mediated Barbier-type allylation of aldehydes compared to other conventional solvents. It plays the dual role of a solvent and a metal activator enabling higher yields of the products in a shorter reaction time using stoichiometric/near-stoichiometric amounts of reagents. Plausibly, [bmim][Br] activates Bi metal by a charge transfer mechanism. The 1H VT-NMR studies suggested that both the allylating species, allylbismuth dibromide and diallylbismuth bromide, are generated in situ.
Highlights
The metal-mediated Barbier-type allylation of aldehydes has drawn considerable attention, because the resultant homoallylic alcohols are versatile intermediates for natural product synthesis [1-7]
room temperature ionic liquid (RTIL) are conceived as eco-friendly solvents due to their low vapor pressure, high stability towards air, moisture and heat, ability to dissolve various substrates, and their reusability [11-14]
In order to investigate whether species I and II are in equilibrium, we added BiBr3 (1 mmol) in a stirred mixture of Bi (1 mmol), allyl bromide (1.2 mmol) in [bmim][Br] (2 mL), stirred for additional 0.5 h, and 1H NMR spectrum of an aliquot taken from the reaction mixture was recorded in CD2Cl2 at −70 °C
Summary
The metal-mediated Barbier-type allylation of aldehydes has drawn considerable attention, because the resultant homoallylic alcohols are versatile intermediates for natural product synthesis [1-7]. We screened different solvents and metal activators (chemical additives and ultrasonication) for the Bi-mediated allylation of benzaldehyde (1a), as the model substrate with commercially available and inexpensive allyl bromide (Scheme 1) at room temperature (25 °C) [39-42].
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