Preparation of allylic lithium reagents with the allylic system partly incorporated into carbocyclic rings

Article abstract of DOI:10.1016/S0022-328X(00)99451-8

A new method is described for preparation of allylic type organolithiums in which two of the allylic system carbons form part of carbocyclic ring.It involves cleavage of the readily accessible allylic sulfides 1-phenylthiomethylcycloalkanes by the naphthalenelithium in tetrahydrofuran.Carbonation of the reagents has given mixtures of cycloalken-1-yl acetic acids and 2-methylecycloalkane carboxylic acids, the distribution of which is strongly dependent on the ring size; thus the proportion of cycloalkenyl acetic acid, the endocyclic olefinic product, increases sharply on going from C5 to C8 ring derivatives and then considerably less sharply on going from C8 to C10 at which point the carbonation reaction has a high selectivity.It is concluded that the site of attack in the allylic anion by CO2 is determined by the thermochemical stability of the product(s).