Chemoselective Oxidation of Alcohols to Aldehydes and Ketones by Iodosobenzene/(Salen) Chromium Complex

Abstract

Various benzylic and allylic alcohols were selectively oxidized to their corresponding aldehydes and ketones by a new Cr(III)(salen) complex I as the catalyst and PhIO as terminal oxidant. The oxidation requires relatively shorter reaction time and produces excellent yields.

benzylic alcohol - allylic alcohol - Cr(salen) - oxidation - chemoselectivity

Reference

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General procedure for preparation of catalyst I : To a suspension of bis(3,5-dicholorosalicylidene)ethyl-enediamine [0.775 g (1.9 mmol)] in 50 mL of absolute THF was added suspension of anhydrous chromous chloride [0.307 g (2.5 mmol)] in THF (30 mL) with vigorous stirring under N₂ atmosphere at room temperature (ca. 20 °C) for 1 h. Then the dark brown solution was allowed to reflux in the presence of air for 2 h. The residue was suspended in water (50 mL) and the undissolved yellowish brown color material was collected by filtration and washed with water (3 ¥ 10 mL). After filtration and concentration of the filtrate with evaporator, brown material was precipitated on cooling overnight, which was collected and dried under reduced pressure to afford 0.86 g of the required complex I (yield; 93%), mp 320-325 °C, IR (KBr): 3071, 1615, 1440, 1168, 869 cm^-1. Anal. Calcd. for C₁₆H₁₀Cl₅CrN₂O₂: C, 39.1; H, 2.05; N, 5.7. Found: C, 38.9; H, 2.2; N, 5.4.