Substituent-control of two modes of intramolecular reactions of allyloxy-silyllithiums and propargyloxy-silyllithiums

Intramolecular reactions of the [(allyloxy)silyl]lithiums and the [(propargyloxy)silyl]lithiums have been investigated. The [(allyloxy)silyl]lithiums proceed in two reaction modes depending on the electronic effect of the substituents at the terminus of the oletin. The [(allyloxy)silyl]lithiums bearing hydrogen, n-C6H13 or trmethylsilyl substituent undergo the [2,3]-sila-Wittig rearrangement to afford the lithium allylsilanolates, while those bearing the phenyl, thienyl, or triphenylsilyl substituent experience the 4-exo-trig cyclization Lind subsequent 1,3-cycloelimination to give the lithium cyclopropylsilanolates. On the other hand, the [(propargyloxy)silyl]lithiums preferentially undergo the 4-exo-dig cyclization over the [2,3]-sila-Wittig rearrangement in all cases.