A formate ester, such as ethyl formate, reacts with an...

A formate ester, such as ethyl formate, reacts with an excess of a Grignard reagent to give (after protonation) secondary alcohols with two identical alkyl groups. (a) Propose a mechanism to show how the reaction of ethyl formate with an excess of allylmagnesium bromide gives, after protonation, 1,6-heptadien-4-ol. (b) Show how you would use reactions of Grignard reagents with ethyl formate to synthesize the following secondary alcohols. (i) 3 -pentanol (ii) diphenylmethanol (iii) trans, trans- 2,7 -nonadien- $5-01$

Transcript

00:01 We've got a brief synthesis exercise involving grigniagents that we're going to work through now.

00:11 So first off, just some background, when you react a formate ester like apple formate, which looks like this, with an excess of a greenug reagent, then you would give a secondary alcohol after protonating with two identical alcohol groups.

00:30 So first, we're going to go through the mechanism for how this occurs.

00:35 So you have your, this is just a very, a very abbreviated mechanism for how renugreatation works.

00:44 So you have your magnesium, which is bonded to your alkyl group.

00:50 Let's just go with r for this one.

00:54 And so that is going to coordinate to your oxygen.

00:58 And so that will pull electron density up as your alkali -group attacks the carbonyl carbon.

01:07 And so you will end up with this tetrahedral intermediate.

01:11 So you have your o, magnesium, and then you have your r group here, and then your o -e -t.

01:23 And then what's going to happen is you will have a collapse of your tetrahedral intermediate.

01:28 It, and that will kick off your ethoxy group.

01:33 And so you'll end up with this, and then you have the same thing happen again, where you have another r group that is going to attack, and then you will end up with this alcoxide, o minus, and then r, and then when that gets protonated, you will end up with your secondary alcohol.

02:04 Seems simple enough.

02:06 And so that is part a, our mechanism.

02:12 And so for part b, we have a few different compounds that we want to synthesize using ethel formate.

02:19 So we start with the formate.

02:24 And part b, we have three pentanyl.

02:27 So that's going to be just this...

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