SOME INVESTIGATIONS OF THE CHEMISTRY OF CARENE 259 benzoates shows that the more sterically hindered axial esters are more slowly hydrolysed than their equatorial counterparts (24, 28). (d) Horeau's method (29), in which the preferred enantiomer of a- phenylbutyric anhydride consumed in the esterification of the caranols is determined, leads to a knowledge of the configuration at the carbinol centre. By these methods we arrived at the configurations shown in the form- ulae (1 la, 17a, 20a, 24a, and 26a) for the caranols discussed above. 7 CH2B CH2[• =_ (28) • (2•) ($o} R The methods used for the preparation of the caranols are effective but tedious. It therefore appeared appropriate to apply Brown's iso- merisation reaction (6) to the readily formed cis-caranyl-trans-4-borane (formula 16) with a view to the formation of an equilibrium mixture of the 2-, 4-, and 5-boranes. In the event we found (8) that when the 4-borane (formula 16) was heated, it rapidly isomerised giving a mixture of the boranes mentioned, together with cis-m-menth-4-enyl-8-borane {formula 28) and, if the temperature reached 140 ø, cis- and trans-caranyl-lO-boranes (formulae 29, 30) were also formed. Oxidation of the mixture of borane isomers with alkaline peroxide gave a mixture of (--)-cis-caran-trans-2-ol (formula 11), (--)-cis-caran-trans-4-ol (formula 17), (--)-cis-caran-trans-5-ol (formula 24), (--)-cis-m-menth-4-en-8-ol (formula 31), and a mixture of cis- and trans-caran-10-ols (formula 32 R, [i-, a- CH20H). The results of these experiments are shown graphically in Fig. 8. The speeds of formation of the boranes (identified as their alcohols) are shown in Fig. 4. The formation of the unsaturated monocyclic borane (formula 28) probably takes place by 1,4- addition of boron hydride to the a, [i- un- saturated cyclopropane system of (--)-cis-car-4-ene (formula 21) formed as

260 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS intermediate, as portrayed below. A similar 1,4- hydroboronation occurs with a- gurjunene (30). HO•' _-- The identity of (--)-cis-m-menth-4-en-8-ol (formula 31) was confirmed by its preparation from (+)-cis-caran-cis-5-ol (formula 26), by pyrolysis (11, 31) and by reaction with 0.1N hydrochloric acid (8). The acid cata- lysed reaction takes place as shown below. H, x f U + ioo % 50 (24) (11) (32, t{, [•-, ct- CH2OH) (31) 20 50 I10 150 170 Temperature, øC Figure 3. Approximate compositions of the alcohol mixtures from the oxidafire hydro- boronarian of (+)-car-3-ene (formula 2) at different temperatures.