Sulphonate esters rearrangements involving

The Beckmann and similar rearrangements are technically outside the scope of this review, since they involve rearrangement with loss of the sulphonate group. Moreover, for obvious reasons such rearrangements are not limited to sulphonate esters. Nonetheless, mention must be made here of these reactions since the formation of sulphonate esters from oximes is a common method of activation in order to carry out the Beckmann rearrangement. 

The Neber rearrangement of oxime sulphonate esters (equation 28) is a useful method for the synthesis of a-aminoketones78. The reaction is base catalysed and involves abstraction of the most acidic proton a to the oxime functional group, as exemplified by the exclusive formation of compound 40 in this rearrangement (equation 29). 

Intramolecular alkylation of an a-sulphonyl anion in the methyl sulphonate ester 53 is potentially possible. Though the rearrangement (equation 40) is observed, deuterium labelling experiments reveal that the reaction involves intermolecular methyl transfer104. This is attributed to the preference of SN2 reactions for backside attack at the tetrahedral carbon atom. 

Selective removal of bromine from 3/3,5,6/3-tribromo-5a-cholestane to give 3/3-bromocholest-5-ene was achieved by reaction with [T -C5H5Cr(N02)2]2. The reactions of 11/3-hydroxy-steroids with dialkylaminosulphur trifluorides depend on the substitution at C-9 and involve the formation of intermediate (11) (Scheme 1) (see ref. 232). Selective dehydration with FeCls adsorbed on silica gel allowed the conversion of 5a-cholestane-3/3,5-diol into cholesterol (80%) and 3i3-acetoxy-5a-cholestane-5,25-diol into 3/S-acetoxycholest-5-en-25-ol (72%). Other examples and additionally the hydrolysis of 5,6a-epoxy-5o -cholestan-3/3-ol to the 3/3,5a,6/8-triol (90%) were reported. Chromatographic alumina is reported to effect smooth elimination of sulphonic acids from the esters with less than normal rearrangement. Thus lanosteryl tosylate and cycloartenyl tosylate gave the respective A -compounds in yields of 90% and 45% respec-... 

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