A spirocyclic chroman from a spiroepoxycyclohexadienone

Reaction between the hydroxymethylspiroepoxycyclohexadienone (2) and chlorotrimethylsilane gave the spirocyclic chroman (3) whose crystal structure has been determined. The chroman presumably arose by dimerisation of an intermediate o-quinone methide (5). The stereochemistry of the chroman (3) in solution is also considered.