Comments for Org Prep Daily

Comment on Intramolecular Carboacylation with rhodium C-C insertion by Cru Jones

Cru Jones — Mon, 16 Nov 2009 02:32:18 +0000

I have used Aldrich-bought MnO2 for simple alcohol oxidations, and it worked quite well without any prior activation. I did, however, use powdered 4A molecular sieves that were stored in a 110 °C oven. It greatly improved the reaction for me, but I don’t know how general it is. Also, still used 10 equiv of the oxidant, so for scale this will probably be a problem.

Comment on Intramolecular Carboacylation with rhodium C-C insertion by milkshake

milkshake — Sun, 15 Nov 2009 17:56:25 +0000

I think its from JACS 131(2) (2009) 412-3.

http://pubs.acs.org/doi/abs/10.1021/ja8066308

You can ask Chris Douglas here about it

Comment on Intramolecular Carboacylation with rhodium C-C insertion by MattW

MattW — Sun, 15 Nov 2009 16:07:53 +0000

Can you provide a a ref. for 1 to 2?

Comment on Intramolecular Carboacylation with rhodium C-C insertion by Ed

Ed — Fri, 13 Nov 2009 07:21:42 +0000

I’ve always used Fluka MnO2 – never had any trouble. Then again, its always been used on pretty robust substrates where 15-20 eq. could be used no problem at all!

Comment on Intramolecular Carboacylation with rhodium C-C insertion by milkshake

milkshake — Thu, 12 Nov 2009 23:48:23 +0000

I think not because permanganate is even a stronger oxidant and it is fully compatible with pyridine (in fact some permanganate oxidations of poorly soluble substrates use pyridine as a co-solvent). BaMnO4 is commercial but I remember a long time ago we made it by combining 1 equiv of NaOH and 1 equiv of BaCl2 with aqueous KMnO4 solution and then adding slowly 0.125 eq of KI solution (as a reducing agent, it goes all the way up to periodate) and BaMnO4 falls out as a dark-green solid.

Comment on Intramolecular Carboacylation with rhodium C-C insertion by Chris Douglas

Chris Douglas — Thu, 12 Nov 2009 23:25:08 +0000

We did bake our Aldrich swag in the oven (125 C), but no luck.

Forgot about BaMnO4 – might be easier in the work-up than IBX. think we need to worry about quinoline N-oxide formation with that?

Comment on 8-bromoquinoline – a painless Skraup synthesis by Chris Douglas

Chris Douglas — Thu, 12 Nov 2009 23:18:33 +0000

One other minor comment on the procedure. The listed order of addition isn’t critical to the success of the rxn (aside from the glycerol), but it makes your life a lot easier. make sure the MeSO3H is hot and stirring when you add the bromoaniline. otherwise the nice bromoaniline crystals from Acros form a big solid mass at the bottom of your 3-neck, caked around your stir-rod, taking forever to dissolve. Even the big Arrow overhead stirrer wouldn’t budge.

Other than that little speed-bump, this was the nicest Skraup I’d ever seen.

Comment on Intramolecular Carboacylation with rhodium C-C insertion by milkshake

milkshake — Thu, 12 Nov 2009 23:14:50 +0000

I once re-activated a lazy bottle of MnO2 by just spreading the stuff in a wide dish and placing it into a glassware-drying oven at 110-120C overnight, then letting it cool in a closed bottle. MnO2 is like Al2O3 – it gets deactivated by moisture. Also it works better in non-polar solvents like benzene.

The dried stuff in my hands was a lot faster with farnesol as a substrate but the reaction mix was less clean and I saw more cis/trans C=C isomerization of the product also. I wonder if anyone tried to add powdered sieves to MnO2 oxidations – people use sieves with TPAP/NMO (and PDC as well) but I have not seen it with MnO2.

(Then there is BaMnO4, an alternative to MnO2 thats made from permanganate quite easily.)

Comment on Intramolecular Carboacylation with rhodium C-C insertion by Chris Douglas

Chris Douglas — Thu, 12 Nov 2009 23:02:36 +0000

I wanted to use MnO2, but we had really mixed results with that. A homemade batch we borrowed from the Hoye lab worked great, but others (like the stuff from Aldrich and Acros in particular) did absolutely nothing. The literature preps for “active” MnO2 didn’t look to fun. Anyone have a favorite way to prep that reagent?

Comment on 8-bromoquinoline – a painless Skraup synthesis by milkshake

milkshake — Thu, 12 Nov 2009 11:39:07 +0000

I think Fe oxidation catalyst is in there for this purpose – it is probably some sorta stepwise single electron oxidation