Question

Draw the products of these 4 dienes with maleic anhydride. Provide the melting point of the adduct as well. Thank you.

CH3 β-myrcene M.P. Diels-Alder product: 33-34 CH3 CH3 M.P. Diels-Alder product: 60-61° α-phellandrene M.P. Diels-Alder allo-ocimene M.P. Diels-Alder product: 83-84° product: 126-127

Answer 1

Diels-Alder reaction is a [4+2] cycloaddition reaction of a conjugated diene and an alkene (dienophile). It is a stereospecific reaction giving rise to syn addition products. When different regio or stereoisomers are possible, the product which is sterically most favoured in transition state and/or in final product, is predominantly formed.

Diels-Alder addition of alpha-terpinene and maleic anhydride gives endo product. endo product is favoured due to pi-interactions between diene and C=O group of maleic anhydride.

Similarly, Diels-Alder addition of alpha-phellandrene and maleic anhydride gives endo product.

The products are shown in the image uploaded.