1. (1S,2S,4R)-3,3-Dichloro-4,8,12,12-tetra-methyl-tricyclo-[5.5.0.0]dodeca-6,8-diene
Ahmed Benharref, Lahcen El Ammari, Moha Berraho, Esaadia Lassaba Acta Crystallogr Sect E Struct Rep Online. 2010 Aug 28;66(Pt 9):o2463. doi: 10.1107/S1600536810034070.
The title compound, C(16)H(22)Cl(2), a derivative of β-himachalene, was semi-synthesized from natural essential oils of Cedrus atlantica. The mol-ecule is built up from two fused six- and seven-membered rings. The six-membered ring has a perfect chair conformation, whereas the seven-membered ring displays a screw boat conformation; the dihedral angle between the rings is 46.48 (9)°.
2. (2S,4R)-4-Ammonio-5-oxopyrrolidine-2-carboxylate
Krzysztof Kaczmarek, Jakub Wojciechowski, Wojciech M Wolf Acta Crystallogr Sect E Struct Rep Online. 2010 Mar 13;66(Pt 4):o831-2. doi: 10.1107/S1600536810004277.
In the crystal structure of the title compound, C(5)H(8)N(2)O(3), the mol-ecules exist in the zwitterionic form. The pyrrolidine ring adopts an envelope conformation with the unsubstituted endocyclic C atom situated at the flap. The other four endocyclic atoms are coplanar with the exocyclic carbonyl O atom, with an r.m.s. deviation from the mean plane of 0.06 Å. The carboxyl-ate substituent is located axially, while the ammonium group occupies an equatorial position. In the crystal structure, the mol-ecules are linked through N-H⋯O hydrogen bonds, forming a three-dimensional network.
3. Synthesis of methyl N-Boc-(2S,4R)-4-methylpipecolate
Kuo-Yuan Hung, Paul W R Harris, Margaret A Brimble J Org Chem. 2010 Dec 17;75(24):8728-31. doi: 10.1021/jo102038q. Epub 2010 Nov 23.
An efficient stereoselective synthesis of fully protected (2S,4R)-4-methylpipecolic acid has been developed. The synthesis was achieved by initial asymmetric α-alkylation of glycine with a chiral iodide, affording the linear precursor as a single stereoisomer. Subsequent aldehyde formation using OsO(4)/NaIO(4) followed by immediate intramolecular cyclization afforded an enamine that was then subjected to hydrogenation to give the final compound in 23% yield over 10 steps.
