Pyridine-sulfonic anhydride, adduct

Sulfur compounds have also been widely studied as activating agents for polyesterification reactions. p-Toluenesulfonyl chloride (tosyl chloride) reacts with DMF in pyridine to form a Vilsmeir adduct which easily reacts with carboxylic acids at 100-120° C, giving highly reactive mixed carboxylic-sulfonic anhydrides.312 The reaction is efficient both for aromatic dicarboxylic acid-bisphenol312 and hydroxybenzoic acid314 polyesterifications (Scheme 2.31). The formation of phenyl tosylates as significant side products of this reaction has been reported.315... 

Furansulfonic acid176 provides an example Pure furan, b.p. 31.2-31.5°, is prepared from technical furan by way of the maleic anhydride adduct, which is then decomposed at 140 to 150°. This furan is treated with the pyridine-sulfur trioxide adduct in a bomb-tube for 8-10 h at 100°. This product is treated with a paste of barium carbonate in water for 30-40 min, then filtered hot, and concentrated, and the barium sulfonate is precipitated by ethanol. The following yields are obtained from 1.9 g of furan with 4.4 g of pyridine-sulfur trioxide 30%, with 8.8 g 56%, and with 13.4 g 90%, S-Benzylthiouronium 2-furansulfonate melts at 205°. 

The aziridine aldehyde 56 undergoes a facile Baylis-Hillman reaction with methyl or ethyl acrylate, acrylonitrile, methyl vinyl ketone, and vinyl sulfone [60]. The adducts 57 were obtained as mixtures of syn- and anfz-diastereomers. The synthetic utility of the Baylis-Hillman adducts was also investigated. With acetic anhydride in pyridine an SN2 -type substitution of the initially formed allylic acetate by an acetoxy group takes place to give product 58. Nucleophilic reactions of this product with, e. g., morpholine, thiol/Et3N, or sodium azide in DMSO resulted in an apparent displacement of the acetoxy group. Tentatively, this result may be explained by invoking the initial formation of an ionic intermediate 59, which is then followed by the reaction with the nucleophile as shown in Scheme 43. 

Quaternary amonium salts [796], tertiary amines or pyridines [797], bicyclic tertiary amines, cryptants [798] or amphoteric alkylamino sulfonates [799] are suitable as accelerators for this 3-component esterification. Liberation of the aldehyde 280 from its depot form, the bisulphite adduct, may taken place under the reaction conditions in a hydrocarbon [800] or better in ethyl acetate [801]. In order to minimize the occurrence of side products, keeping the aqueous phase more alkaUne for removal of the casually produced small amounts of pyrethroid acid anhydride 305 [802] is recommended. More expedient is the activation of such anhydrides by 4-dimethyl-... 

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