Die 1,1‐Carboborierung von Bis(alkinyl)phosphanen als Zugang zum Phospholgerüst

Abstract

Wir danken der Deutschen Forschungsgemeinschaft für die Fçrderung unserer Arbeit. J.M. dankt der NRW Research School (Universität Münster) für ein Stipendium. K.U. dankt JSPS und der International Research Training Group Münster/Nagoya für ein Stipendium und Unterstützung. Hintergrundinformationen zu diesem Beitrag sind im WWW unter http://dx.doi.org/10.1002/ange.201107398 zu finden.

Unusual Pathway Taken in the Reaction of Bis(alkynyl)diisopropylaminoboranes with B(C6F5)3

“…We and others had previously shown that siloles [2,8] or phospholes [9] can readily be obtained by a series of consecu- In any case, hydride transfer from the diisopropylamino substituent to the distal carbon atom of the second [B]-acetylene substituent represents the favored pathway to give the products 10. These show a framework similar to that of the compound type B mentioned in the introduction (see Scheme 1), but it is has been formed in quite a different reaction sequence.…”

“…We and others had previously shown that siloles2, 8 or phospholes9 can readily be obtained by a series of consecutive 1,1‐carboboration reactions starting from the respective bis(alkynyl)silanes or ‐phosphanes. The bis(alkynyl)aminoborane 7 /B(C 6 F 5 ) 3 systems investigated in this study could have offered a similar pathway to borole systems.…”

“…[5,6] We had recently shown that 1,1-carboboration reactions can be facilitated by employing strongly electrophilic RB-A C H T U N G T R E N N U N G (C 6 F 5 ) 2 reagents (e.g., R = C 6 F 5 or alkyl). [7,8] We have extended the application range of the 1,1-carboboration sequence to converting bisalkynyl phosphanes 2 into the respective phosphole derivatives 3 (see Scheme 2) by using B-A C H T U N G T R E N N U N G (C 6 F 5 ) 3 as the borane reagent, [9] and we have used BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 for dihydroborole syntheses (e.g., 4 to 6). [10,11] This posed the question whether the reaction of a dialkynylborane derivative with BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 might take a similar course that might eventually lead to the formation of a borole derivative.…”

“…However, this resulted in the formation of products that remotely resembled the five-membered het-Abstract: The bisA C H T U N G T R E N N U N G (alkynyl)diisopropylaminoboranes 7 were prepared by treatment of iPr 2 NBCl 2 with two molar equivalents of 1-pentynyl lithium or lithium phenylacetylenide, respectively. Their reaction with one molar equivalent of BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 resulted in the formation of the 1,1-carboboration products 8 that were subsequently stabilized by adduct formation (9) with tert-butyl isocyanide. Thermolysis of 8 a (R = nPr) proceeded with hydride transfer from a N-isopropyl substituent to the distal carbon atom of the remaining pentynyl unit at boron to give the zwitterionic five-membered heterocyclic product 10 a in good yield.…”

“…We had recently shown that 1,1‐carboboration reactions can be facilitated by employing strongly electrophilic RB(C 6 F 5 ) 2 reagents (e.g., R=C 6 F 5 or alkyl) 7. 8 We have extended the application range of the 1,1‐carboboration sequence to converting bisalkynyl phosphanes 2 into the respective phosphole derivatives 3 (see Scheme ) by using B(C 6 F 5 ) 3 as the borane reagent,9 and we have used B(C 6 F 5 ) 3 for dihydroborole syntheses (e.g., 4 to 6 ) 10. 11…”