Cyclisation versus 1,1-Carboboration: Reactions of B(C6F5)3 with Propargyl Amides.
A series of propargyl amides were prepared and their reactions with the Lewis acidic compound B(C6F5)3 were investigated. These reactions were shown to afford novel heterocycles under mild conditions. The reaction of a variety of N-substituted propargyl amides with B(C6F5)3 led to an intramolecular oxo-boration cyclisation reaction, which afforded the 5-alkylidene-4,5-dihydrooxazolium borate species. Secondary propargyl amides gave oxazoles in B(C6F5)3 mediated (catalytic) cyclisation reactions. In the special case of disubstitution adjacent to the nitrogen atom, 1,1-carboboration is favoured as a result of the increased steric hindrance (1,3-allylic strain) in the 5-alkylidene-4,5-dihydrooxazolium borate species.
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6 (Canada).
Rebecca L
RL
Melen
Max M
MM
Hansmann
Alan J
AJ
Lough
A Stephen K
AS
Hashmi
Douglas W
DW
Stephan
D000480:Alkynes / Q000737:chemistry*; D000577:Amides / Q000737:chemistry*; D001896:Boron Compounds / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D015394:Molecular Structure
D000480:Alkynes; D000577:Amides; D001896:Boron Compounds
1,1‐carboboration; alkynes; boron; cyclization; oxazoles; propargyl amides