ok, _Organic Syntheses_ roulette time again
the word of the day is "distinct"
http://orgsyn.org/demo.aspx?prep=v96p0245
*winces* this is a very new one, and I've been hoping not to have to comment on it because it's sufficiently complicated to defy any easy explanation, and because the aim of the synthesis is so _specific_
I've complained before that O.S. methods used to be ones of great generality but I suppose they've run out of easy targets
here's the full title
Synthesis of Chiral Diamine Ligands for Nickel-catalyzed Asymmetric Cross-couplings of Alkylchloroboronate Esters with Alkylzincs: (1R,2R)-N,N'-Dimethyl-1,2-bis(2-methylphenyl)-1,2-diaminoethane
yeah. soak that one in
synthesis of an ingredient of a chiral catalyst meant to be used for one very specific coupling reaction between organoboron and organozinc reagents
like, I think about wanting to do this sort of chemistry every time I get out of bed in the morning
I'll just name a couple features of the synthesis
the chiral ligand being synthesized is a vicinal diamine, i.e. a derivative of ethylenediamine, H₂NCH₂CH₂NH₂. vicinal diamines tend to be excellent ligands for transition metals, such as nickel, here
the molecule is a symmetrical one! it's chiral in the same way that tartaric acid is chiral
there's some kinda odd Cope-type rearrangement in the first step that breaks a carbon-carbon bond and makes a new one, in a concerted fashion
methyls are tacked onto the unsubstituted vicinal amino groups by an odd procedure, but one I think that insures that the nitrogens get one methyl each. direct methylation of the nitrogens (e.g. with methyl iodide) would probably yield the tetramethylated product chiefly, or if you could stop the reaction at disubstitutions, you'd get one dimethylamino group and one unsubstituted one
instead, ethyl chloroformate is used to tack on carbethoxy groups, which are then reduced to methyl with LiAlH4