Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: ice on July 09, 2007, 04:36:38 PM
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Hi all,
Does anyone have any experience with this condensation reaction? It appears to be quite tricky with temperature control and often people use 4x excess azide (in EtOH/EtONa). However, literature yields range from 90+ all the way down into the 20's for reasons that I really don't understand.
The reaction works in my hands but not well at all and I wondered what's going on here. It seems like a great way to introduce some very useful functionality but it seems very tricky. . . .
I've been using various conditions but the "best" (ha!) is usually: to a -10 EtOH/EtONa (4 equivalents Na) solution is added 4:1 azide/aldehyde mixture (neat) dropwise and then stir at ~-10 for 3-4 hours. Longer times do not appear to increase yields, neither does adding more EtONa/EtOH and azide. I was wondering if anyone tried tBuOK/THF or some other base combination at lower temperatures. . .I would not have chosen a protic solvent for this reaction but what do I know. . .
Any and all help appreciated! :)
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i would wonder whether you are getting some enolisation of your aldehyde under those conditions, followed by allsorts of nasty side reactions (aldehyde aldehyde aldol etc). Has anyone used some more reasonable conditions? (ie. for an ester-aldehyde condensation i'm doing, i cool LDA/THF down to -78 degC (1.3 eq dry diisopropylamine and 1.2 eq titrated BuLi), add 1.4 eq ester, stir at -78, add 1 eq aldehyde, stir 1 hr at -78, quench with NH4Cl and workup). I would give these conditions (or similar reported ones) a go.