Pyridinium p-toluenesulphonate

The rearrangement which involves the intermediacy of the same cyclopropylcarbinyl cation (138) is completed in few minutes as monitored by t.l.c. Upon treatment with 10 mol % of pyridinium p-toluenesulphonate (PPTS) in ethanol at 55°C in order to cleave the protective group, some tetrahydropyranyl ethers of conjugated dienols (140) or enones (141) have undergone total C3 - C4 ring enlargement (equation 102) ... 

Pyridinium p-toluenesulphonate in methanol at reflux has been shown to be effective in selective removal of the isopropylldene groups of 1, 6-anhydro-2,3-0-isopropylidene-/d-D-mannopyrano3e derivatives bearing 4.-0-allyl, -tert-butyl, -trichloroacetyl, and -tert-butyldi-phenylsilyl groups. 

From the reaction of D-galactitol with 2,2-dimethor ropane in dimethyl sulphoxide catalysed by pyridinium p-toluenesulphonate the diacetonides (2) and (3) have been isolated. From the latter, the 1,3 2,4 5,6-tri-O-isopropylidene derivative (4) was obtained on treatment with fresh reagents. The structures of these new acetals were established spectrometrically and their possible role in the conventional isopropylidenation of D-galactitol has been assessed. ... 

Hydrolysis of the diethylacetal function employing p-toluenesulphonic acid in acetone, pyridinium p-toluene-sulphonate in EtOH, and a suspension of Si02 in hexane. In all cases the corresponding aldehyde is obtained in high yield as a Z E isomeric mixture. Transmetallation of acetal with Me2Cu(CN)Li2 followed by treatment with c-hexenones giving the 1,4-addition product. Alternatively, transmetallation with n-BuLi and reaction with benzaldehyde giving the expected alcohol. 

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