Novel approach to 3,3-dimethyl-4-morpholino-3,4-dihydrocoumarins via hetero-Diels–Alder reaction

A new four-step synthetic procedure has been developed to prepare 3,3-dimethyl-4-morpholino-3,4-dihydrocoumarins from substituted salicylaldehydes, morpholine, and isobutyraldehyde. It involves aminal formation, deamination, enamine formation, hetero-Diels–Alder reaction, hydrolysis, and oxidation. The aminal formation, subsequent one-pot domino deamination, enamine formation, and hetero-Diels–Alder reaction were achieved in microwave-assisted catalyst-free conditions. The following hydrolysis and oxidation steps, performed conventionally, gave quantitative yields.

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