Stereo- and regiochemistry in the (asymmetric) cycloaddition reaction of 5-chloro-2(1H)-pyrazinones with cyclic and monosubstituted alkenes and with a N-acryloyl substituted chiral auxiliary

Add time:08/29/2019    Source:sciencedirect.com

The cycloaddition of 5-chloro-2(1H)-pyrazinones 1 with various dienophiles was used to generate the corresponding 2,5-diazabicyclo[2.2.2]octanes. Following reduction or hydrolysis of the bridged adducts, the regio- and stereochemical structure was determined by analysis of the coupling and NOE patterns in the 1H NMR spectra. With symmetric dienophiles the endo adducts are formed exclusively. The regiochemistry for the reaction of 1 with methyl acrylate and ethyl vinyl ether, and the asymmetric induction found with the N-acryloyl substituted chiral auxiliary (4S)-4-isopropyl-1-methyltetrahydro-2H-imidazol-2-one, largely depend on the electron donating or attracting properties and size of the 3-substituents of 1.

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