Viva la Phosphene
For those keeping score at home, it’s been Carbon-Carbon Bond Forming Reaction: 10, Jeremy: 0. I’ve come home the past few weeks with a sweaty forehead after my nitroethylene unexpectedly flash-polymerized in a plume of NO2 (I’ve been told by my inorganic cohorts that a little bit of NO2 is “good for ya” once in a while). Fate has taken a turn recently, though; the University finally repaired the severed fiber optic cable behind the science library finally allowing me to use SciFinder.
I literally stumbled onto my proverbial four-leafed clover (something that probably would’ve happened sooner had the construction crews excercised a bit more caution with the jackhammer, see above). In the preparation of a number of nitro-containing substrates, Watanabe et al. (Hel. Chim. Acta 1984, 67, 1204-1207) disclosed that trialkylphoshpines are capable of activating already highly reactive substrates (i.e. nitroethylene) to facilitate pseudo-conjugate addition reactions via substitution mechanism. In short, it’s a variation of the Rauhut-Currier reaction (US Patent 3,074,999 1963) or Baylis-Hillman with a twist (alkylphosphines instead of DABCO). The best part is that the reaction mixture is pretty mild in terms of pH and therefore can tolerate a number of highly reactive olefins; the proof is seen in the new TLC spot this morning that matches up against my known standard and the fact that I haven’t seen one nanomole of nitrogendioxide gas.
WHAT? To the layman, think of the reaction as TNT that you’re trying to light with a match but no fuse. You’ll inevitably blow yourself up when the match touches the highly explosive material. Now, think of the alkylphosphine as a detonation switch similar to what Wile E. Coyote uses to blow up the Road Runner in Bugs Bunny cartoons. This charge source is reusable and suits other major purpose of not blowing yourself up (or tanking your reaction).
The Rauhut-Currier reaction has been applied in numerous instances. While I won’t highlight the several applications, I will say that there’s an excellent, well-cited review about the Rauhut-Currier reaction by Michael Bultman (works with David Gin at the Sloan-Kettering Institute in NY): http://chemistry.uiuc.edu/gradprogram/chem435/fall04/07_Bultman_Abstract.pdf
