A New Julia-Type Reagent for Methylenation Reactions

1-Methyl-2-(methylsulfonyl)benzimidazole (1) is a sulfone derivative developed of its application by Ando et al. which is used as a Julia-Kocienski-type methylenation reagent. 1 reacts with aldehydes and ketones to afford the methylene moieties under mild conditions in one pot. In the methylenation reaction, Wittig reagent is often used but one equivalent of triphenylphosphine oxide is obtained as a by-product which is hard to remove. Therefore the Wittig reagent is unsuitable for use on a large scale. On the other hand, the benzimidazole derivative as a by-product in this reaction is able to be removed by partition, so that the purification can be done more easily.

Experimental procedure: to a solution of 1 (0.076 g, 0.36 mmol) and p-methoxyacetophenone (0.045 g, 0.30 mmol) in DMF (1.5 mL) under argon is added tert-BuOK (0.101 g, 0.90 mmol) at room temperature. After stirring for 1 h, the reaction is quenched with an aqueous NH₄Cl solution and the mixture is extracted with AcOEt (2 x 10 mL). The combined extracts are washed with H₂O (3 x 10 mL), brine, dried (MgSO₄), and concentrated. Column chromatography (silica gel;" hexane : AcOEt = 10 : 1) provides 2-(4-methoxyphenyl)propene (0.041 g, 92%) as a colorless solid.