16. Conjugated Systems

Predict the product of the following [2 + 2] cycloadditions.

(a)

Use FMOT to predict the mechanism and products for the following cycloaddition. If no product is favored, write “symmetry-disallowed” in place of the product.

Use the cycloaddition summary rules to verify that you have come to the correct conclusion.

Show that the [4 + 2] Diels–Alder reaction is photochemically forbidden.

Will a concerted reaction take place between 1,3-butadiene and 2-cyclohexenone in the presence of ultraviolet light?

Draw the product of each of the following reactions:

g.

Show what product would result from the [6 + 2] cycloaddition of hexa-1,3,5-triene with maleic anhydride.

The [2 + 2] cyclization is especially useful when done intramolecularly. 

(a) What makes intramolecular reactions more favorable? 

(b) Predict the product of the following cyclization (slight modification of a reaction from Angew. Chem. 2011, 50, 5149)

Draw the product of each of the following reactions:

h.