Identify the major product of the following reaction.

Step-by-step solution

The reaction involves an intramolecular nucleophilic attack by a thiolate anion on an epoxide ring. First, sodium hydride (NaH) acts as a strong base and deprotonates the thiol (-SH) group to form a highly nucleophilic thiolate anion (-S^-). The molecule has a chain of four carbon atoms between the sulfur atom and the epoxide ring. The epoxide is a cis-epoxide, with the alkyl chain and the methyl group on the same side (both wedged in a standard representation). The thiolate anion can attack either carbon of the ep