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 carbondioxide in a retro-Diels–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.
Solution 38SP
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.
