Question

Question. The following reaction resembles the acid-catalyzed cyclization of squalene oxide. Propose a mechanism for this reaction.

Short answer

Epoxide ring is highly strained due to which it readily opens up so as to release strain, thus oxygen in epoxide ring abstracts acidic proton from acid, and oxygen acquires positive charge due to which strain on ring further increases, hence it opens up and alkene carbon which is electron rich acts as a nucleophile and is present in same system thus intramolecularly attacks at carbocation generated.

Abstraction of proton and attack of nucleophile at carbocation

Step-by-step solution

Step-1. Abstraction of acidic hydrogen and ring opening of squalene oxide:

Epoxide ring is highly strained due to which it readily opens up so as to release strain, thus oxygen in epoxide ring abstracts acidic proton from acid, and oxygen acquires positive charge due to which strain on ring further increases, hence it opens up and alkene carbon which is electron rich acts as a nucleophile and is present in same system thus intramolecularly attacks at carbocation generated.

Abstraction of proton and attack of nucleophile at carbocation

Step-2. Attack of water as a nucleophile at carbocation and formation of product:

Water acts as a nucleophile and attacks at carbocation center, then after neutralization of positive charge on oxygen, we get our required product, that is, 3-hydroxymethyl-1-methyl-cyclopentan-1-ol.

Attack of water as a nucleophile and formation of final product