Chapter 12, Problem 12.61P

Interpretation Introduction

Interpretation:

The missing compounds in the given sequence of reactions are to be supplied.

Concept introduction:

Alkenes undergo electrophilic addition reactions with molecular halogens like ${\text{Cl}}_{\text{2}}{\text{ and Br}}_{\text{2}}$ peroxy acids ${\text{(RCO}}_{\text{3}}\text{H)}$, carbenes (${\text{R}}_{\text{2}}\text{C:}$), and borane (${\text{BH}}_3$). In all these reactions, the mechanism involves a transition state which is cyclic and does not go through the formation of a carbocation. As a carbocation is not formed, the regioselectivity and the stereochemistry of such reactions is important.

An epoxide can be produced from an alkene using a peroxy acid ${\text{(RCO}}_{\text{3}}\text{H)}$, also called peracid. Most often, meta-chloroperbenzoic acid (MCPBA) is used as a peroxy acid. This reaction preserves the cis/trans relationships of the groups attached to the alkene. Epoxide ring opens when an epoxide undergoes nucleophilic substitution reactions under basic, neutral, or acidic conditions. Under basic or neutral conditions, the nucleophile attacks the least substituted carbon atom of the epoxide.

Alcohols undergo acid-catalyzed dehydration reactions via E1 mechanism to yield a three-membered ring with the insertion of an oxygen atom, that is, epoxide.

Diazomethane, when heated in the presence of light, generates a carbene.

A carbene adds to an alkene via a three-membered transition state to produce a cyclopropane ring. This reaction also preserves the cis/trans relationships of the groups attached to the alkene carbons.