2015
DOI: 10.1021/acs.organomet.5b00753
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Pathways to Functionalized Heterocycles: Propargyl Rearrangement using B(C6F5)3

Abstract: The reactions of propargyl amides, ureas, carbamates, and carbonates with B(C 6 F 5 ) 3 proceed via an intramolecular 5-exo-dig cyclization across the alkyne unit to yield the corresponding vinyl borate species. The generated sp 2 carbocation is stabilized by the flanking heteroatoms, allowing for isolation of oxazoline intermediates. The fate of these intermediates is strongly dependent upon the propargylfunctionalized starting material, with the carbamates and carbonates undergoing a ring-opening mechanism (… Show more

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Cited by 29 publications
(40 citation statements)
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“…Alternatively,b orane activation of the alkyne followed by a1 ,2-trans-oxyboration reaction with subsequent proto-or carbodeboration could occur (pathway II,S cheme 6). Both pathways have been observed in other reactions with B(C 6 F 5 ) 3 .F or example,w eh ave previously noted the deprotection of Boc groups using catalytic amounts of B(C 6 F 5 ) 3 , which is reminiscent of pathway I, [20] while oxyboration pathway II has also been observed in studies by ourselves [20,21] and others [10b, 22] in the synthesis of oxazoles,d ioxaborinines, pyryliums,and lactones.…”
Section: Angewandte Chemiementioning
confidence: 65%
“…Alternatively,b orane activation of the alkyne followed by a1 ,2-trans-oxyboration reaction with subsequent proto-or carbodeboration could occur (pathway II,S cheme 6). Both pathways have been observed in other reactions with B(C 6 F 5 ) 3 .F or example,w eh ave previously noted the deprotection of Boc groups using catalytic amounts of B(C 6 F 5 ) 3 , which is reminiscent of pathway I, [20] while oxyboration pathway II has also been observed in studies by ourselves [20,21] and others [10b, 22] in the synthesis of oxazoles,d ioxaborinines, pyryliums,and lactones.…”
Section: Angewandte Chemiementioning
confidence: 65%
“…Substantial recent work has shown that the highly electrophilic B(C 6 F 5 ) 3 can activate alkynes towards nucleophilic cyclization. 14 The resulting zwitterionic heterocycles, however, contain a carbon–B(C 6 F 5 ) 3 bond, which is unreactive for the rich downstream Suzuki cross-coupling reactivity of boron (example, Figure 1a 3 ). This limits their utility as synthetic building blocks.…”
Section: Introductionmentioning
confidence: 99%
“…Unsere Gruppe führte mit katalytischen Mengen des Borans eine Boc-Entschützung durch, die mechanistisch an Reaktionspfad I erinnert. [20] Jedoch auch der zweite Reaktionspfad II wurde von unserer [20,21] und anderen [10b,22] Gruppen in der Synthese von Oxazolen, Dioxoborininen, Pyrilium-Salzen und Lactonen bereits beobachtet. …”
Section: Bindungsbildung Mit B(c6f5)3 üBer Kationische Zwischenstufenunclassified