X- THE POSSIBILITY OF CHIRAL INDUCTION IN THE TRANSFER PROCESS( TRANSFER FROM THE HALONIUM IONS OF ADAMANTYLIDENEADAMANTANE TO ACCEPTOR OLEFINS )

The bromonium ion of adamantylideneadamantane (Ad=Ad-Br+) has been use d to induce the bromocyclization of a 4-pentenyl glycoside (10) and a 5-hexenyl glycoside (11) in dichloroethane. The kinetics of these proc esses have been studied at 25 degrees C in the presence of varying [Ad =Ad] and, in the case of the transfer to 10, in the presence of pentan ol. The second-order rate constants for bromocyclization of these two alkenes are (1.04 +/- 0.06) x 10(-1) M-1 s(-1) and (5.34 +/- 0.2) x 10 (-2) M-1 s(-1) respectively, and in no case does added Ad=Ad or pentan ol alter the reaction rate. The kinetic behavior is interpreted in ter ms of cyclization occurring directly from a 1:1 complex of Ad=Ad-Br+ a nd 10 or 11. The chiral induction for the bromocyclization of 10 promo ted by AdAd-Br+ was measured at 20% e.e., the (-)-(S)-tetrahydrofurfur yl bromide being the dominant stereoisomer. Ad=Ad molecules substitute d at one of the homoallylic carbons by an axial methyl group (12), or by two methyl groups (axial and equatorial), were synthesized and the H-1 NMR spectra of their bromonium ions is given. These materials are not stable for prolonged times at room temperature. A limited kinetic study of the reaction of 12-Br+ and 4-pentenol indicated that the Brtransfer is 500 times faster than the comparable transfer from Ad=Ad-B r+ to 4-pentenol. The possibility of using these materials to induce c hiral bromocyclization is discussed.