Glycol monotosylate

Base catalyzed pinacol rearrangement of vicinal m-glycol monotosylates is a simple and useful general method for preparing perhydroazulenes. Thus, treatment of cholestane-5a,6a-diol 6-tosylate (115a) with either one mole-equivalent of potassium t-butoxide in f-butanol at 25° or with calcium carbonate in dimethylformamide at 100° gives a quantitative yield of 10(5 6/5H)... 

Fig. 14.19. First semipinacol rearrangement of a glycol monotosylate. The reaction involves three steps in neutral media formation of a carbe-nium ion, rearrangement to a carboxonium ion, and deprotonation to the ketone.

Fig. 14.20. Second semipinacol rearrangement of a glycol monotosylate. The reaction involves two steps in basic media, since the [l,2]-rear-rangement and the dissociation of the tosylate occur at the same time. Under reaction conditions this rearrangement is followed by a base-catalyzed epimerization. This is why instead of the initially cis-annulated bicyclic ketone D its trans-isomer C is isolated.

The stereospecific preparation of cis- and tra s-oxiranes can be achieved from the same diol via the acetal. The trans-oxirane is obtained via the glycol monotosyl ester and the c/s-oxirane via the bromohydrin ester (Eq. 53). ... 

Pinacol-type rearrangement of glycol monotosylates Ring contraction... 

Triethylamine Regiospecific formation of glycol monotosylates via cyclic dialkoxystannanes Nucleoside deriys. 

---