Bradsher reaction mechanism

An arenium ion is an intermediate in this reaction, and the last step involves the dehydration of an alcohol. Propose a plausible mechanism for this example of the Bradsher reaction. 

For Ri = R2 = H, alkyl, the reaction is classified as the proper Bradsher reaction. If R2 = aryl, the variation has been classified as the Vingiello process. There has been some discussion in the literature as to the mechanistic pathway for these variations and two mechanisms remain to... 

Uses. Tetramethylene sulfone has high solvent power for aromatics and has been used extensively by Olah and co-workers for Friedel-Crafts type nitrations and for studies of the mechanism of nitronium tetrafluoroborate nitration of alkyl-benzenes and halobenzenes in homogeneous solution. It is a superior solvent for quaternization of tertiary amines with alkyl halides, since it has a high dielectric constant and does not enter into side reactions observed with nitrobenzene and dimethylformamide. For example in the synthesis of the acridizinium salt (3), Bradsher and Parham effected quaternization of (1) with benzyl bromide in tetramethylene sulfone at room temperature in excellent yield. Several other salts analagous to (2) were obtained in good yield and in crystalline form with use of tetramethylene sulfone, whereas with other solvents the products were colored... 

The mechanism for forming acridizinium salt is similar to the Bradsher Cyclization when a carbonyl group exists in the reaction system. However, the mechanism for forming oxazole[3,2-a] pyridinium is different from what is proposed here. 

---