Abstract
A number of allylsilanes were synthesized and their reactions with allyldichloroboranes were studied. The stereochemistry and scope of this new allylboration reaction have been determined. These new allylboration reagents are useful because of their greatly increased reactivity compared to triallylboranes. Allyldichloroborane and methallyldichloroborane showed similar reactivity to each other, but crotyldichloroborane was less reactive than the other two dichloroboranes when reacted with allylsilanes. Addition of allyldichloroboranes to allylsilanes is in a syn, regiospecific fashion. Allylboration with these new reagents is stereospecific for cyclic allylsilanes, while fairly diastereoselective for acyclic allylsilanes. The reaction is controlled by both steric and electronic effects of substituents. The reaction worked very well with unhindered allylsilanes such as allylsilane (21), 3-trimethylsilyl-1- butene (25) and (2,4-pentadienyl)trimethylsilane (28). A fairly good yield was found with y-substituted allylsilanes, such as in crotylsilane (27), 3-trimethylsilylcyclopentene (29) and 3-trimethylsilylcyclohexene (30). The reaction worked less well in cases where steric effects greatly blocked the approach of the allyl group as in methallyltriethylsilane (22). The reaction did not work in cases where the carbon-silicon bond was more susceptible to side reactions than the carbon-carbon double bond to allylboration as in 5-trimethylsilylcyclopentadiene (34), or where allylsilanes were simply not reactive enough as in 3- trimethlysilycycloheptane (32), 3-trimethylsilycyclooctene (33), and cinnamyltrimethylsilane (26h, 27b).
Zhang, Zongren (1995). Allylboration of allylsilanes with allyldichloroboranes. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -Z463.