DAT bootcamp Orgo question

[JDHK]

http://datbootcamp.com/wp-content/uploads/2013/03/Q16Question1.jpg

That's the link to the question. The answer says

Adding a Grignard reagent to an ester results in a total of TWO additions of the reagent and a final product of a tertiary alcohol. The first CH3MgBr will add to the electrophilic carbonyl in the ester, forming an alkoxide. However, at this point in such strongly basic conditions, the –OR group in the ester is an acceptable leaving group. This means it will leave, resulting in the formation of a ketone (product E). Finally, another CH3MgBr will add to the ketone resulting in product A.

I am aware of how the grignart reagent works, but the qusetion I have about this is the part where it says "however at this point in such strongly basic conditions". I assumed the OR group leaves because there was no answer choices with it in it, but I'm just wondering for future reference, where in this reaction is there such "Strong basic conditions?". i looked up THF, and it's a weak base.

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[koutarou]

Grignards are always strongly basic! (They're strong nucleophiles, right?) That's just something that you need to remember. The reasoning behind it is that the Mg of the Grignard has a partial positive charge, which then forces the carbon of the Grignard to take on a partial negative charge, making it pretty basic. Hope this somewhat cleared this up for you!