INVESTIGATIONS IN THE SYNTHESIS OF RETINOIDS .2. ACETYLATION OF DIOLINE C-20 AND DIOL C-20

The conversion of the two glycols dioline C20 (Ia, 2-cis-3,7-dimethyl-9-(2;6;6'-trimethyl-1'-cyclohexene-1'-yl)-2,7-nona-diene-4-yn-1,6-diol) and diol C20 (IIa, 2,4-dicis-3,7-dimethyl-9-(2;6;6'-trimethyl-1'-cyclohexene-1'-yl)-2,4,7-nonatriene-1,6-diol) has been studied in the presence of various acylating and catalyzing agents with a view to defining a variant that allows Ia and IIa monoacetates or their diacetates with a high conversion of the parent Ia and IIa diols to be obtained. The routine procedures were used to acetylate hydroxy groups in the presence of organic bases (triethylamine, pyridine) in benzene or methylene chloride with acetyl chloride and acetic anhydride, as well as with acetic anhydrate and catalytically added cobalt chloride. The highest yield was obtained when acylation was effected by using acetic anhydride in the presence of organic bases. The higher reactivity of dioline C20 resulted in higher selectivity and yield than that of diol C20.