[darkdevil]

Hi there,
Suppose I have this compound, 3-bromobenzaldehyde

And I want to substitute the bromo group with an alkyl group. I am not sure which method I shall use??
1) Suzuki coupling with alkyl broronic acid
2) Protect the aldehyde and then do grignard and then treat with alkyl halide
3) Organoaluminum method
4) others??

[Archer]

No.2 won't work, Grignard reagents don't undergo S_N2 reactions.

I would try Suzuki coupling if I were attempting this.

[AlphaScent]

I have done 10-undecyn-1-OTHP grignard addition to 1-bromo-3-pentyne at low temperatures with success. Albeit higher temps resulted in elminination. 

[AlphaScent]

You now what.  I believe I misspoke.  Grignards do not go through Sn2.  I forgot about our good friend Copper's involvement in my reaction.  That is sure not Sn2.  I was wrong.

[Archer]

I have done 10-undecyn-1-OTHP grignard addition to 1-bromo-3-pentyne at low temperatures with success. Albeit higher temps resulted in elminination.

Ah, ok, I have never tried this for simple C-C bond formation.

[zsinger]

NO DOUBT SUZUKI COUPLING!  I will caution you though if you have never done it……read about it like you were a novice before you try it again, as I screwed it up about 4 times before success (and I had done it in undergrad)! 

[Archer]

You now what.  I believe I misspoke.  Grignards do not go through Sn2.  I forgot about our good friend Copper's involvement in my reaction.  That is sure not Sn2.  I was wrong.

I did wonder why this worked if a Grignard underwent S_N2 readily then they would form only in very low yields because as they formed they would react with the starting material present.

[darkdevil]

NO DOUBT SUZUKI COUPLING!  I will caution you though if you have never done it……read about it like you were a novice before you try it again, as I screwed it up about 4 times before success (and I had done it in undergrad)!

I failed once already.
I dont know how to make the boronic acid from like 1-bromooctane..
What I did was making a 1-bromooctane grignard first, and then treated with triisopropylborate. And then I just added  3-bromobenzaldehyde with the Pd(Oac)2 catalyst and stirred at r.t for one day.

[Dan]

You may encounter stability problems with alkylboronic acids/esters. An alkyl tetrafluoroborate will probably be better. Check out the work of Gary Molander, he's developed some nice methods for alkylating aryl halides.

You may also want to consider Negishi coupling.

[orgopete]

Since you seem to actually be trying this reaction, I'd also consider doing a Heck reaction and reductive the product.

Or, use an acetylene with copper catalyst and reducing as per AlphaScent's suggestion.