mercredi 2 mai 2007

Synthesis of 2-Ethyl-1,2,3,4-tetrahydroquinoxaline

In 2006, Lectka et al. described the synthesis of quinazolinones by a catalytic, enantioselective hetero-Diels-Alder reaction. The key point of this synthesis is the double activation of the diene (diazadiene) in one hand and the dienophile in the other hand.
Activation of o-Benzoquinone diimide (diene) has been achieved by zinc (II) triflate, whereas activation of ketene enolate (dienophile) by benzoylquinidine starting from corresponding acide chloride. This reaction has been performed in THF at -78°C to give a single enantiomer (%ee >99) in 76% yield. Finally the reduction of both benzoyl group and quinoxalinone with LiAlH4 has provided the 2-Ethyl-1,2,3,4-tetrahydroquinoxaline, which is an inhibitor of cholesteryl ester transfer protein.

Ref: J. AM. CHEM. SOC. 2006, 128, 13370-13371

For the synthesis of o-Benzoquinone diimide see:
J. Am. Chem. Soc. 1954, 76, 2763-2769.