Formation of iodides and esters from alcohols and tributyldiiodophosphorane and diiodotriphenylphosphorane

Tributyldiiodophosphorane and diiodotriphenylphosphorane, prepared in situ from the corresponding phosphine and iodine, are generally able to convert primary and secondary alcohols into iodides at room temperature in diethyl ether or benzene containing two equivalents of hexamethylphosphoric triamide. Tertiary alcohols, as gauged by the lack of reactivity of t-butyl alcohol, are, however, inert to these iodinating agents. 6-Hydroxyhexanoic acid yields a mixture of 6-iodohexanoic acid and 7-heptanolide. The first reagent also promotes facile condensation of secondary and tertiary alcohols with carboxylic acids to form hindered esters in good yields. The phosphorane derived from tris-(dimethy1amino)phosphine and iodine, while less effective as an iodinating agent, rapidly converts 6-hydroxyhexanoic acid into 6-iodo-N,N-dimethylhexanamide, and hexanoic and benzoic acids into the corresponding N,N-dimethylamides in excellent yields at room temperature. Treatment of 3β- tosyloxycholest-5-ene with lithium iodide yields 3β-iodocholest-5-ene, and not 3α-iodocholest-5-ene, as previously reported.