Cyclopentadiene, addition hydroxylation

The relatively low percentage of ring substitution can be attributed to several side reactions 1,4-addition of Li to 2-cyclopentenone, incomplete dehydration of 4 as evidenced by the presence of a small hydroxyl absorption (3425 cm ) in the IR spectrum of 5, and reduction of the polymer-bound cyclopentadiene in its reaction with Co2(C0)8 (26,27,32). 

Hydroxylation by hydrogen peroxide in t-butyl alcohol solution is catalyzed by osmium tetroxide. The catalyst is volatile and dangerous to handle but is conveniently used in a solution of the tertiary alcohol. The yields of diols are usually low (30-60%), and the process has not been adapted to large-scale preparations. In contrast to hydroxylation by performic acid, this procedure leads to cis addition of the two hydroxyl groups to the double bond. An extensive study of other catalysts has been made. Some catalysts, e.g., selenium dioxide and pertungstic acid, catalyze addition in the trans direction. Hydroxylation of cyclopentadiene takes place in the 1,4-positions to give 2-cyclopenten-l,4-diol. ... 

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