“…For example, the reaction of acetal 4a with (24), followed by hydrolysis of the acetal group and hydration of the triple CºC bond in 25, afforded unsaturated aldehydoester 26 which is structurally related to mevalonic acid [17,23] (Scheme 8). D,L-5-[ 13 C]-Mevalonolactone was obtained by reaction sequence including condensation of acetal 4a with ethyl acetate in liquid ammonia in the presence of lithium amide to ethyl 1-[ 13 C]-3-hydroxy-5,5-dimethoxy-3-methylpentanoate (27), reduction of the ester group in 27 to hydroxy with lithium tetrahydridoaluminate, removal of the acetal protection from diol 28, oxidation of the aldehyde group to carboxylic with bromine in water, and lactonization of the resulting hydroxy acid [17,23] (Scheme 9).…”