[robvba]

Will treating 6-bromo-1-phenylbutanal with

1. Ph3P/THF
2. t-BuOK

produce any product?

thank you

[sjb]

What are your thoughts? How will the phosphine react with your starting material?

[lutesium]

Open the case a little more so that we can help you!!!


Lutesium...

[robvba]

This is for my Orgo class.
The starting reagent is 6-bromo-1-phenylhexanal (sorry, its hexa not buta)

the first step in the reactions is to add Ph3P/THF

the second step is to add tert-BuOK

so what will be the product?

I cant see Ph3P reacting with the carbonyl as there is nothing attached to it (Ph3P)
however, in the second step, i think the tert-BuOK will strip the Bromine from the hexanal and form a double bond.
If that is the case, the question is, will this react with the cabonyl to form a ring maybe? There are only enough hydrogens for a ring with a double bond.

[sjb]

Not the carbonyl (directly, at least). What else is there?

There are only enough hydrogens for a ring with a double bond.

What do you mean by this?

S

[alexjaco]

Look up the Wittig Reaction and you should be able to figure out what happens.  You are creating an ylide with the phosphine followed by base.

[robvba]

Not the carbonyl (directly, at least). What else is there?

There are only enough hydrogens for a ring with a double bond.

What do you mean by this?

S

i meant that if the 6-bromo-1-phenylhexanal were to somehow form a ring, it would have to be a ring with a double bond because there are currently only 10 hydroges and we do not have a reagent that provides us with additional H+

[robvba]

Look up the Wittig Reaction and you should be able to figure out what happens.  You are creating an ylide with the phosphine followed by base.

i'm somewhat familiar with the witting reaction. however, as far as i know, a ylide is created when there is something attached to PPh3 (C=PPh3).
Also, if phosphine is PH3, where is it in this reaction?

do you mean that the PPh3 will strip the bromine off of 6-bromo-1-phenylhexanal and react with the carbonyl to form a ring with a doube bond (attached to the phenyl ring?)

[alexjaco]

1- PPh₃ reacts with the carbon attached to the bromine, in an S_N2 fashion
2- The base deprotonates the proton on the newly formed carbon-phoshine bond to form the ylide
3- The ylide reacts with the carbonyl (Wittig) to form a cyclic alkene and triphenylphospine oxide (by-product)

If this doesnt make sense, I can try to post a mechanism rather then words.

[robvba]

1- PPh₃ reacts with the carbon attached to the bromine, in an S_N2 fashion
2- The base deprotonates the proton on the newly formed carbon-phoshine bond to form the ylide
3- The ylide reacts with the carbonyl (Wittig) to form a cyclic alkene and triphenylphospine oxide (by-product)

If this doesnt make sense, I can try to post a mechanism rather then words.

thank you. this is the product i had in mind, only i wasnt sure how to get there as i dont have much experience with PPh3. The mechinism makes sence. Thank you for offering ot post it. Only i still have a hard time picturing how the bulky PPh3 could get close to anything.

[alexjaco]

Yea, I know what you mean, even though its quite large, its still a good nucleophile.  Check out the link below, its a reaction to create an ylide for the Horner-Wadsworth-Emmons reaction, which is very closely related to the Wittig, just different selectivity and more options, but it shows the nucleophilicity of a similar phosphine.

http://www.organic-chemistry.org/namedreactions/arbuzov-reaction.shtm