Well, over the last week or so I have been struggling to form this damn strecker product on a particularly bitchy aldehyde (read F@rking HORRIBLE). Anyway, after failing miserably numerous times I have decided to modify my aldehyde to make it a bit more stable and possibly allow me to follow some literature procedure a bit more closely.
Unfortunately, this means PCC (pyridinium chlorochromate) yummy! and the boss wants me to use this due to the literature. I am seriously not cool with the whole thing. I mean seriously, Ley's oxidation was working quite well on the less stable compound and is a bit less nasty. But anyway, I have to admire the simplicity in setting up a reaction of this sort. Reminds me of cooking a little bit.
Not that I taste my reaction or anything but I mean the whole way it is just like measure out the ingredients (Alcohol, Molecular sieves, Dry DCM, PCC) and then bung them all together, sonicate and stir. There is barely any fussing around, just have to be careful weighing out the PCC and then you just spoon it into the stirred solution of sieves and alcohol in DCM (~0.05-.25M).
The workup is a bit of a bitch cuz you have all that nasty nasty floating around but you really just have to add some silica and some Ether and filter through some silica, wash it and then move on to column or just take it through to the next step. Pretty nice, but at the same time kinda deadly, like a portugese man of war. Anyway, time to "Get in the Lab". Wooh! Gotta love slave labor as a PhD student. $4/hr is a totally amazing pay rate! (SARCASM!)
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Oooooh, wait till you use mercury or organotin. At least with chromium you can reduce it to chromium 3. Mercury is nasty no matter what oxidation state and you can't really reduce organotin... treating it with fluoride is as good as it gets, but only works if there's a leaving group on the tin
ReplyDeletesome people pay a lot of money for metabolic enhancing chromium supplements ;)
ReplyDeleteWhat kind of cyanide source do you use for Strecker? TMS-CN is quite nice if you take the precautions (=volatile cyanide source). Also if your aldehyde craps up with amines (which is common trouble with imines from aliphatic aldehydes) you can make cyanohydrine first (TMSCN, 1mol% of ZnI2, 0C) and then throw in an excess of amine with 2 eqivs of acetic acid, and heat it up, it should convert to Strecker product.
ReplyDeleteAlso, for large-scale reactions especially with lazy substrates like aniline and ketone (I used 4-piperidone as the carbonyl piece) I had good results with working in acetic acid as a solvent at 10C and spooning in Zn(CN)2 as a solid.
Yeah TMSCN (What a biatch!) but I am suuuuppppeeerrr careful. I have tried a few methods but have not used glacial acetic. I did try using Yb(OTf)3 as a lewis acid to drive it though that didn't work. My aldehyde is just a turd, I will have to try harder to push it through.
ReplyDelete