Organocatalyzed enantioselective protonation of silyl enol ethers: scope, limitations, and application to the preparation of enantioenriched homoisoflavones.
In the present work, enantioselective protonation of silyl enol ethers is reported by means of a variety of chiral nitrogen bases as catalysts, mainly derived from cinchona alkaloids, in the presence of various protic nucleophiles as proton source. A detailed study of the most relevant reaction parameters is disclosed allowing high enantioselectivities of up to 92% ee with excellent yields to be achieved under mild and eco-friendly conditions. The synthetic utility of this organocatalytic protonation was demonstrated during the preparation of two homoisoflavones 4a and 4b, isolated from Chlorophytum Inornatum and Scilla Nervosa, which were obtained with 81% and 78% ee, respectively.
Laboratoire de Chimie Organique Bio-organique Réactivité et Analyse (COBRA), CNRS UMR 6014 & FR 3038, Université et INSA de Rouen, Rue Tesnière, Mont-Saint-Aignan 76130-F, France.
Thomas
T
Poisson
Vincent
V
Gembus
Vincent
V
Dalla
Sylvain
S
Oudeyer
Vincent
V
Levacher
D002384:Catalysis; D002930:Cinchona Alkaloids / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry*; D007529:Isoflavones / Q000737:chemistry*; D015394:Molecular Structure; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism
D002930:Cinchona Alkaloids; D004987:Ethers; D007529:Isoflavones; D012821:Silanes