(A true story.) 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 water workup, they found that the product was a mixture
of two compounds. One was the expected product having
two ethyl groups, but the unexpected product had added
three ethyl groups. Propose a mechanism to explain
the formation of the unexpected product.
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