1,2,3-Triphenyl-1,2,3-trithexylcyclotrisilanes: Synthesis and ring-opening by halogens

Article abstract of DOI:10.1246/bcsj.71.2449

Reaction of dichlorophenyIthexylsilane (thexyl =1,1,2-trimethylpropyl) with lithium naphthalenide in tetrahydrofuran at -65 °C gave cis,cis- and cis,trans-1,2,3-triphenyl-1,2,3-trithexylcyclotrisilane 1 (cis,cis-1 and cis, trans-1) in yields of 19 and 52%, respectively. The structures of both isomers were determined by X-ray crystallography. The ring-opening reaction of each isomer with bromine leads to the formation of 1,3-dibromo-1,2,3-triphenyl-1,2,3-trithexyltrisilane (2); cis,cis-1 gave only (1R.3R)/(1S,3S)-1,3-dibromo-1,2,3l-triphenyl-1,2,3-triuiexyltrisilane ((1R,3R)/(1S,35)-2) (87% yield). While cis, trans-1 formed (1R,2s,3S)- and (1R, 2r, 3S)-1,3-dibromo-1,2,3-triphenyl-1,2,3-trithexyltrisilane ((1R,2s,3S)-2 and (1R,2r,3S)-2, in 13 and 31% yields) as well as (1R,3R)/(1S/3S)-2 (44% yield). The structures of (1R,3R)/(1S,3S)-2 and (1R,2r,3S)-2 were confirmed by X-ray crystallography. From the stereochemical results observed in the ring-opening reactions, it is concluded that the cleavage of the Si-Si bonds occurs with retention-inversion of the configuration of the silicon atoms. In the chlorination, cis,cis-1 gave (1R,3R)/(1S,3S)-1,3-dichloro-1,2,3-triphenyl-1,2,3-trithexyltrisilane ((1R, 3A)/(1S,3S)-3, 40% yield) and (1R,2r,3S)-1,3-dichloro-1,2,3-triphenyl-1,2,3-trithexyltrisilane ((1R,2r,3S)-3, 30% yield); cis,trans-1 gave (1R,3R)/(1S.3S)-3 (33% yield), (1R,2r,3S)-3 (14% yield), and (1R,2s,3S)-1,3-dichloro-1,2,3-triphenyl-1,2,3-trithexyltrisilane in 40% yield. The structure of (1R,2r,3S)-3 was confirmed by X-ray crystallography. The result indicates that stereoselectivity was lower in the ring-opening by chlorine than in that by bromine.