Part of a synthesis by E. J. Corey and David Watt (Harvard University) involves the Diels-Alder cycloaddition of the following pyrone and cyclohexenone. The initial reaction gives the endo product, which loses carbon dioxide in a retroDiels-Alder to generate a diene with predictable stereochemistry and functionality. IR and UV spectroscopy of the final product show that it contains a diene conjugated with an ester, and an unconjugated ketone. Determine the structures of the intermediate and the final product, with particular attention to their stereochemistry.
Diels-Alder reaction is a concerted reaction between a diene and a dienophile. It usually results in the formation of new six-membered ring.
Example: 1,3-butadiene undergoes cycloaddition reaction with ethylene (diene) to form a cyclohexene. This reaction takes place through a six membered cyclic transition state. The reaction as follows:
Treatment of methyl 2-oxo-2H-pyran-3-carboxylate with 4-methylcyclohex-3-enone gives the following Diels-alder product.
Step 3 of 3
Decarboxylation of the Diels-alder product gives the following diene in the product.