Werner, Markus et al. published their research in Liebigs Annalen in 1996 | CAS: 28322-40-9

Isopentyltriphenylphosphonium bromide (cas: 28322-40-9) belongs to organobromine compounds. Bromine is more electronegative than carbon (2.9 vs 2.5). Consequently, the carbon in a carbon–bromine bond is electrophilic, i.e. alkyl bromides are alkylating agents. When the molecular ion is detected, the bromine and chlorine isotope patterns are very distinct, but caution is to be exercised for certain mixed chlorinated/brominated compounds, which can look similar to homohalogen patterns.SDS of cas: 28322-40-9

Synthesis of [1.1.1]propellanes by bridging of bicyclo[1.1.0]butanes was written by Werner, Markus;Stephenson, David S.;Szeimies, Guenter. And the article was included in Liebigs Annalen in 1996.SDS of cas: 28322-40-9 This article mentions the following:

Various [1.1.1]propellanes I [R = H, R1 = alkyl or aryl; R, R1 = Me, Et; RR1 = (CH2)3, (CH2)4] were prepared by bridging the 1,3 positions of the corresponding bicyclo[1.1.0]butane. The synthesis of 1-bromo-3-(chloromethy)bicyclobutanes and the bridging were carried out in a 1-pot reaction by addition of 2 equivalent of MeLi to appropriate 1,1-dibromobis-2,2-(dichloromethyl)cyclopropanes II. Three routes to the cyclopropanes were investigated. The Wittig reaction of 1,3-dichlorocycloacetone leading to RR1CC(CH2Cl)2, was with exception of RR1CC(CH2Cl)2 [RR1 = (CH2)3] successful only with Wittig reagents derived from primary alkyl halides. Reduction of alkylidenemalonates with LiAlH4 in benzene afforded carbinols of type RR1CC(CH2OH)2 which were converted into chlorides by reaction with N-chlorosuccinimide/Me2S. The cyclopropanation of RR1CC(CH2Cl)2 to cyclopropanes II was achieved by reaction with CHBr3/NaOH under phase transfer catalysis conditions. Starting from alkylidenemalonates, the sequence of reduction and cyclopropanatioon was interchanged. Propellanes I (R = H; R1 = Pr, CH2CHMePr) were reduced with LiAlH4 to give the corresponding bicyclo[1.1.1]pentanes. Very small coupling constants J(13C-13C) between the bridgehead positions (i.e. 0.47 and 0.53 Hz) were obtained by 2D inadequate NMR of I (R = H; R1 = CH2CHMeEt, CHMeEt). In the experiment, the researchers used many compounds, for example, Isopentyltriphenylphosphonium bromide (cas: 28322-40-9SDS of cas: 28322-40-9).

Isopentyltriphenylphosphonium bromide (cas: 28322-40-9) belongs to organobromine compounds. Bromine is more electronegative than carbon (2.9 vs 2.5). Consequently, the carbon in a carbon–bromine bond is electrophilic, i.e. alkyl bromides are alkylating agents. When the molecular ion is detected, the bromine and chlorine isotope patterns are very distinct, but caution is to be exercised for certain mixed chlorinated/brominated compounds, which can look similar to homohalogen patterns.SDS of cas: 28322-40-9

Referemce:
Bromide – Wikipedia,
bromide – Wiktionary