TETRAHEDRON LETTERS Tetrahedron Letters 44 (2003) 9055–9056 Pergamon SiBr 4 /wet silica gel as an efficient heterogeneous system for cleavage of CN Surya Kanta De Department of Chemistry, University of Washington, Seattle, WA 98195, USA Received 27 August 2003; revised 24 September 2003; accepted 25 September 2003 Abstract—A new and efficient method for the cleavage of oximes, hydrazones and semicarbazones has been achieved with SiBr 4 /wet silica gel. © 2003 Elsevier Ltd. All rights reserved. Oximes, hydrazones and semicarbazones are useful protecting 1 groups and are extensively used for purifica- tion and characterization of carbonyl compounds. Their synthesis from non-carbonyl compounds 2 pro- vides an alternative pathway to aldehydes and ketones. There has been considerable interest in the development of mild techniques for the conversion of oximes into their corresponding carbonyl compounds. 3–5 Although some of the known methods are carried out under mild reaction conditions, most of them require drastic condi- tions, high temperature, long reaction times, expensive, toxic or not readily available reagents, they need to be freshly prepared and tedious work-up procedure. Recently, some microwave irradiation techniques have been developed 6,7 which are valuable from the synthetic standpoint but extreme precaution have to be taken as these reactions were perfomed under microwave irradi- ation or ultrasonic irradiation with an oxidant. Most of the known methods deal for the regeneration of car- bonyl compounds from oximes only, a little attention has been paid for the regeneration of carbonyl com- pounds from hydrazones and semicarbazones. 8–10 Table 1. Deprotection of oximes, hydrazones and semicarbazones with SiBr 4 /wet silica gel at room temperature Entry Yield a (%) Product Time (min) Substrate 4-Chloroacetophenone semicarbazone 10 4-Chloroacetophenone 93 1 Benzophenone semicarbazones 18 2 Benzophenone 91 24 3 Acetophenone Acetophenone semicarbazone 86 4 4-Methoxyacetophenone semicarbazone 14 4-Methoxyacetophenone 89 5 Benzaldehyde semicarbazone 17 Benzaldehyde 83 87 3-Nitrobenzaldehyde 22 6 3-Nitrobenzaldehyde semicarbazone 7 4-Bromobenzaldehyde semicarbazone 15 4-Bromobenzaldehyde 89 Cyclohexanone semicarbazone 14 8 Cyclohexanone 90 88 4-Methoxybenzaldehyde 18 9 4-Methoxybenzaldehyde semicarbazone Benzophenone phenylhydrazone 26 10 Benzophenone 87 15 4-Chloroacetophenone 11 91 4-Chloroacetophenone phenylhydrazone 4-Bromobenzaldehyde phenylhydrazone 19 12 4-Bromobenzaldehyde 90 2-Nitrobenzaldehyde phenylhydrazone 28 13 2-Nitrobenzaldehyde 79 Cyclohexanone oxime 16 14 Cyclohexanone 85 15 Acetophenone oxime 83 b Acetophenone 220 16 280 Benzophenone oxime Benzophenone 89 b 17 Benzaldehyde oxime 68 Benzaldehyde 90 18 4-Bromobenzaldehyde oxime 35 4-Bromobenzaldehyde 87 a Yields refer to pure isolated products, characterized by IR, 1 H NMR and MS. b Under reflux condition. 0040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2003.09.208