P-Toluenesulfonic anhydride

Enolizahon of cyanoketone rac-5 under the previously optimized conditions, followed by reaction with p-toluenesulfonic anhydride afforded a 90 10 ratio of the two expected enol tosylates in 90% yield. An immediate advantage of the tosylates compared to the triflate was seen on isolation, when the desired compound 32 was found to be a crystalline solid. In this way an 85% isolated yield of 32 as a single isomer could be achieved without the need for chromatography (Scheme 9.24). Use of p-toluenesulfonyl chloride in place of the anhydride led to a-chlorination... 

Product distributions obtained on esterification of nucleosides and nucleotides under basic conditions throw further light on factors affecting selective reactivity. p-Toluenesulfonylation of adenosine 5 -monophosphate in aqueous alkali yielded exclusively (in 54-61% yield) the 2 -p-toluenesulfonate.107 Lack of reaction at HO-3 was attributed either to formation of a phosphoric p-toluenesulfonic anhydride, which sterically protected this hydroxyl group, or to the higher acidity of HO-2. It has been shown that the acidic site (with pKa 12.5) in adenosine is associated with the presence of both HO-2 and HO-3, as replacement of either of these by hydrogen, or of HO-2 by methoxyl, results in loss of this acidity.108 Inductive effects, or the sta-... 

V-Arylsulfonyiation of primary and secondary amines is usually accomplished with the appropriate sulfonyl chloride in the presence of a suitable base. Both anhydrous [Scheme 8.133)267 and aqueous conditions [Scheme 8.134]288 have been employed. p-Toluenesulfonic anhydride has been employed but its greater cost relegates it to special drcumstances [Scheme 8.135].276... 

Prepared by Robinson condensation of 2,3,5-trimethoxytetrahydro-furan 88, 49) (available from furan), the ketone XXIX gave with subsequent reduction the 6-methoxytropan-3a-ol (XXXII) (see Section III,B) which, in turn, was demethylated by aqueous hydrogen bromide (90%) to (+ )-tropan-3a,6j8-diol (XXXI). As a condensing agent, p-toluenesulfonic anhydride gave good yields of 3a,6a-oxido-tropane (XLVI). 

Indeed, it was the use of partial esterification that enabled the great synthetic exploitation of levoglucosan (6), the most readily accessible 1,6-anhydrohexopyranose. The steric interaction of the axial 3-hy-droxyl group with the 1,6-anhydro bridge is accentuated on reaction with the bulkier acid chlorides or anhydrides in pyridine in such a way that this hydroxyl group is esterified substantially more slowly than the other axially oriented ones. Consequently, the dimolar esterification of 6 with p-toluenesulfonic anhydride,156 benzyloxycarbonyl chloride,520 p-toluenesulfonyl chloride,38 106,156 505 520 636 benzoyl chlo-... 

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