A new protocol for the consecutive alpha- and beta-activation of propiolates towards electrophiles, involving conjugate addition of tertiary amines and intramolecular silyl migration.
Herein, we present a novel approach for the consecutive alpha- and beta-activation of conjugated alkynes and demonstrate the application of this methodology towards the C-C bond-forming reactions of propiolates. This new concept is based on the 1,4-addition of a tertiary amine to a conjugated alkyne, followed by an aldol-type addition to an aldehyde and subsequent intramolecular silyl migration. This sequential process is generally applicable for 3-trimethylsilylpropiolates. The combination of methyl 3-trimethylsilylpropiolate, 1,4-diazobicyclo[2.2.2]octane (DABCO), and aromatic aldehydes brought about domino-type C-C bond formations to afford highly functionalized olefins as the major products. On the other hand, aliphatic aldehydes, including the sterically demanding aromatic aldehyde, 2,6-dimethylbenzaldehyde, produced alkyne derivatives as the sole products from the reaction, presumably, by the reaction pathway common to the first cases. The intramolecular version of the reaction was successfully applied to the cyclization of trimethylsilylpropiolic esters derived from salicylaldehydes, leading to a new formylcoumarin synthesis. Studies of the reaction mechanisms are also described.
Matsuya
Yuji
Y
Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
Hayashi
Kousuke
K
Nemoto
Hideo
H
D000480:Alkynes / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D011422:Propionates / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared
D000480:Alkynes; D000588:Amines; D011422:Propionates; D012821:Silanes; C011537:propiolic acid