5. Chemistry lab students added an excess of ethylmagnesium bromide to methyl furoate, expecting the Grignard reagent to add twice and form the tertiary alcohol. After an aqueous work-up they found that the product was a mixture of two compounds. One was the expected product having two ethyl groups, the unexpected product had added three ethyl groups. Propose a mechanism, including all appropriate arrows, to explain the formation of the unexpected product. OMe xs EtMgBr ether expected OH unexpected OH