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Topic: Thioacetal functionalisation mechanism  (Read 1374 times)

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Offline sggwils2

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Thioacetal functionalisation mechanism
« on: December 04, 2019, 07:46:55 AM »
Can anyone shed any light on the mechanism for this reaction? BuLi will deprotonate at the tertiary centre first before reaction with PhCHO to give the phenyl alcohol. I am now confused as to what role the tert-BuLi plays as it is a sterically hindered strong base suggesting it would favour a second deprotonation followed by SN2 with the MeI but this yields the incorrect product as it seems the tert-BuLi acts as a nucleophile to give the di-substituted Ph/tert-Bu product before the SiMe3 is lost. Any help appreciated. 
« Last Edit: December 04, 2019, 10:02:59 AM by sggwils2 »

Offline clarkstill

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Re: Thioacetal functionalisation mechanism
« Reply #1 on: December 04, 2019, 08:11:13 AM »
I think steps 1-2 will lead to a Peterson Olefination1, you can probably work from there...

[1] https://www.organic-chemistry.org/namedreactions/peterson-olefination.shtm

Offline sggwils2

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Re: Thioacetal functionalisation mechanism
« Reply #2 on: December 04, 2019, 09:59:45 AM »
Noted, thank you. Does this seem a logical reaction mechanism?

Offline clarkstill

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Re: Thioacetal functionalisation mechanism
« Reply #3 on: December 05, 2019, 04:25:05 AM »
That seems like a reasonable proposal given the reagents, but I doubt it'd work in real life - tBuLi is an abysmal nucleophile.

The closest thing I can find in the literature is this: https://www.sciencedirect.com/science/article/pii/S004040390078885X, but in that case the R-Li nucleophile is tethered so the reaction is intramolecular, and it definitely isn't as hindered as tBuLi.

Offline OrganicDan96

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Re: Thioacetal functionalisation mechanism
« Reply #4 on: December 05, 2019, 07:07:02 AM »
tBuLi isn't as bad a nucleophile is you might expect, it apparently reacts via a single electron pathway unlike other alkyllithiums

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