Borata–alkene derivatives conveniently made by frustrated Lewis pair chemistry

Abstract

Two (aryl)PXY starting materials (aryl = mesityl or 2,4,6-triisopropylphenyl; X,Y = Cl, Br) were reacted with lithiated conjugated enynes (derived from 2-methylbutenyne or 1-ethynylcyclohexene) to yield the respective (aryl)bis(enynyl)phosphanes. Their reaction with HB(C6F5)2 gave the heterocyclic five-membered zwitterionic borata-diene compounds containing the aryl group and one unchanged enynyl substituent at phosphorus. The borata-alkene products were thought to arise from a two step process of regioselective alkyne hydroboration followed by an internal phosphane attack on the boryldiene unit. Three examples of the ring-closed borata-alkene type products were characterized by X-ray diffraction.

Zwitterionic Phosphirenium Borates Derived from Bis(alkynyl)mesityl Phosphanes and Tris(pentafluorophenyl)borane

“…We prepared the substituted bis(alkynyl)mesityl phosphanes 5b – 5e analogously. All of these substrates reacted rapidly with a stoichiometric quantity of B(C 6 F 5 ) 3 to form the respective phosphirenium borate zwitterions 6b – 6e (see Scheme and Table ) (for details, see the Supporting Information).…”

Observation of a Thermally Induced Bora‐Nazarov Cyclization at a Phosphole Framework

“…We prepared the bis(alkynyl)phosphane 6 a by treatment of 2,4,6‐triisopropylphenyldihalogenophosphane (TippPX 2 , X=Cl, Br) with the alkynyllithium reagent derived from cyclohexenylacetylene 6. Treatment with one molar equivalent of B(C 6 F 5 ) 3 in pentane at 60 °C (4 h) gave the phosphole 7 a (Scheme ) as an orange solid in 91 % yield.…”

“…We then reacted the analogously prepared6 Tipp‐bis(methylbutenynyl)phosphane 6 b with a small series of RB(C 6 F 5 ) 2 reagents (R=C 6 F 5 , CH 2 CH 2 Ph, CH 3 ). The reaction of 6 b with the parent Lewis acid B(C 6 F 5 ) 3 at RT gave the phosphirenium borate 8 in 87 % yield (Scheme ).…”

Observation of a Thermally Induced Bora‐Nazarov Cyclization at a Phosphole Framework

“…[6] Tr eatment with one molar equivalent of B(C 6 F 5 ) 3 in pentane at 60 8 8C(4h)gave the phosphole 7a (Scheme 2) as an orange solid in 91 %y ield. TheX -ray crystal structure analysis ( Figure 1) showed apentasubstituted phosphole bearing the bulky 2,4,6-triisopropylphenyl (Tipp) group at phosphorus,asingle C 6 F 5 substituent at carbon atom C4, and the remaining B(C 6 F 5 ) 2 unit adjacent at C3.…”

“…We then reacted the analogously prepared [6] Tipp-bis(methylbutenynyl)phosphane 6b with asmall series of RB(C 6 F 5 ) 2 reagents (R = C 6 F 5 ,C H 2 CH 2 Ph, CH 3 ). Ther eaction of 6b with the parent Lewis acid B(C 6 F 5 ) 3 at RT gave the phosphirenium borate 8 in 87 %y ield (Scheme 3).…”