Question

Forward and Retro Diels-Alder Post-Lab Questions: 5-methylfuran-2 (5 H)-one (see below) is an alcohol/water sensitive compound. In the presence of an alcohol, it undergoes a process known as transesterification. Draw the structure of transesterified 5- methylfuran-2(5H)-one: 1. H CHн-он :0: Transesterification -СH3з If the reaction vessel were exposed to methanol during the course of the reflux, would a Diels-Alder reaction also take place with the transesterified dienophile from question 1? Why or why not? Draw the structure of the product formed if the transesterified 5-methylfuran-2(5H)-one were to undergo a Diels-Alder reaction with cyclopentadiene: 2. OH Page 163

Answer 1

The ring opening of 5-methylfuran-2(5H)-one takes place in the presence of methanol. The OCH₃ group of methanol attacks the carbonyl carbon of the lactone ring to form the product methyl-4-hydroxypent-2-enoate. When this product is exposed to methanol during the course of reflux, intramolecular reaction takes place when the hydroxy group (nucleophile) attacks the carbonyl carbon to release the -OCH₃ group and form the stable lactone ring. It can be explained by the following reactions:

HU он mg-bott be con H3C-OH + WCH3 - CH3 5-methylfuran-2(5H)-one methyl-4-hydroxypent-2-enoate H2C OOH - 7° y CH VCH3 + + HCOH H3C-OH CH3

The transesterified product methyl-4-hydroxypent-2-enoate undergoes diels alder reaction with cyclopentadiene.

This can be explained by the following chemical equation:

CooMe COOM HO HO CH3