78 - Organic Chemistry

Question

Heating compound X with aqueous formaldehyde forms Y $\left(C_{17}{H}_{23}NO\right)$ , which has been converted to a mixture of lupinine and epilupinine, alkaloids isolated from lupin, a perennial ornamental plant commonly seen on the roadside in parts of Alaska (Section 25.10). Identify Y and explain how it is formed.

Step-by-Step Solution

Answer

Intramolecular electron transfer

The reaction involving the delocalization of pi-electrons within a compound from an electron-deficient site to an electron-rich site is known as the intramolecular electron transfer reaction.

In the given compound, the pi-electrons are delocalized as the lone pair of electrons on the nitrogen atom of the amine attacks the electrophilic carbon forming a C-N bond. The electron-rich carbon attacks the electrophilic carbonyl carbon, forming a new C-C bond.

            Intramolecular electron transfer in the substrate

Dehydration

The protonated amino group is stabilized as a molecule of it is lost when the lone pair of electrons on the nitrogen atom attacks the electrophilic carbon, resulting in ring closure. 

                                         Ring closure