Question

If the preference for formation of a six-membered ring were not so great, what other cyclic product would be formed from the intramolecular aldol addition of

a.2,6-heptanedione? b. 2,8-nonanedione?

Short answer

a.

b.

Step-by-step solution

Step-by-Step Solution Step 1: Intramolecular aldol   addition of 2,6-heptanedione (a)

The given reactant (a) 2,6-heptanedione is the1,5 diketonethatundergoes intramolecular aldol additions to form a six-membered stable ring (beta-hydroxyketones ),and another cyclic product that can be formed is 4-membered unstable ring when enolate is formed from alpha-carbon which is more close to another carbonyl carbon.

As the preference for the formation of a six-membered ring is not considered, the other cyclic product that is formed is 1-(2-hydroxy-2-methylcyclobutyl)ethanone shown as follows:

Formation of 1-(2-hydroxy-2-methylcyclobutyl)ethanone (a)

Intramolecular aldol  addition of 2,8-nonanedione (b)

The given reactant (a) 2,8-nonanedione is the1,7 diketonethatundergoes intramolecular aldol additions to form a six-membered stable ring (beta-hydroxyketones ),and another cyclic product that can be formed is 8-membered unstable ring when enolate is formed from alpha-carbon which is far from another carbonyl carbon.

As the preference for the formation of a six-membered ring is not considered, the other cyclic product that is formed is3-hydroxy-3methylcyclooctane, and the reaction is shown as follows:

Formation of 3-hydroxy-3methylcyclooctane (b)