INTERMOLECULAR HETERO-DIELS-ALDER REACTIONS OF ENAMINO KETONES WITH HIGHLY SUBSTITUTED VINYL ETHERS EFFECT OF HIGH-PRESSURE ON THE KINETICSAND DIASTEREOSELECTIVITY

The hetero Diels-Alder reactions of enamino ketones 1 and 2 with the v inyl ethers 3-5a are studied in dichloromethane solution under high pr essures up to 5 kbar. The kinetics is measured by on-line FT-IR spectr oscopy up to 3 kbar. The cycloaddition reactions of enamino ketones 1 and 2 with vinyl ethers 3 and 4 yield the diastereomeric dihydropyrans 7a-d and 8a-d, respectively, whereas in the cycloaddition of enamino ketone 1 to vinyl ether 5a the constitutional isomers 9 and 10 are for med. The unexpected reaction of 1 with 5a to give the spiro compound 9 is explained by isomerisation of 5a to 5b under the reaction conditio ns. The kinetics of the reactions is discussed in terms of both overal l and individual rate coefficients, activation energies, and activatio n volumes.