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Jim Simpson

Publications and source records attributed to Jim Simpson.

3 recordsLinked to original sources
PubMed2006

A stereoselective synthesis of 6,6,6-trifluoro-L-daunosamine and 6,6,6-trifluoro-L-acosamine.

A short synthesis of 6,6,6-trifluoro-L-acosamine 15 and 6,6,6-trifluoro-L-daunosamine 19 has been accomplished. The pyranose ring system of these carbohydrate analogues was formed by a hetero-Diels-Alder reaction of vinylogous imide 11 and ethyl vinyl ether which gave adduct 12a in 40% yield. Hydroboration gave 13 and subsequent hydrogenolytic removal of the (R)-2-phenylethyl chiral auxiliary gave ethyl 6,6,6-trifluoro-L-acosaminide 14. Acid hydrolysis furnished target 15. Glycoside 13 was N-trifluoroacetylated to give 16, the structure was confirmed by single crystal X-ray diffraction. The C-4 stereochemistry of 16 was inverted by Swern oxidation of the 4-OH group, and subsequent borohydride reduction to give 17. Hydrogenolytic removal of the auxiliary gave ethyl-6,6,6-trifluoro-L-daunosaminide 18. Acid hydrolysis provided 19.

Fluorine↗
PubMed1998

The Preparation, Stereochemistry and Reactions of Some [Co(cyclen)(NH(3))X](3+/2+) Complexes (X = OH(2), Cl, N(3), OH).

A number of new [Co(cyclen)(NH(3))X](3+/2+) complexes have been prepared (X = OH(2), Cl, N(3), OH), and their stereochemistries, interconversions, and substitution reactions have been explored. All have the syn,anti configuration about the two meridional amine centers of the cis-coordinated cyclen ligand (syn(NH(3)),anti(X)- and syn(X),anti(NH(3))-isomers for X = OH(2), Cl, N(3), OH; designated as 1-X and 2-X respectively) but a syn,syn intermediate is proposed for a number of the reactions. OH(-)-catalyzed hydrolysis (base hydrolysis) dominates the substitution chemistry in aqueous solution (k(OH)/M(-)(1) s(-)(1) values reported) and results from deprotonation at one of the relatively very acidic meridional NH centers (k(H)/M(-)(1) s(-)(1) values reported). A syn orientation of the NH proton in the reactant is considered important in these reactions, with the resulting lone pair assisting in the displacement of X, and with this proton being transferred to X = OH to facilitate an unusually fast and spontaneous solvent replacement reaction (k(ex) = 8 +/- 2 s(-)(1), I = 1.0 M (NaClO(4)), 25 degrees C). Anation by N(3)(-) has been studied, and this proceeds largely via 2-OH for both isomers. A crystal structure of syn(NH(3)),anti(N(3))-[Co(cyclen)(NH(3))N(3)]Cl(0.5)(ClO(4))(1.5). H(2)O is reported; monoclinic, P2(1)/n (No. 14), a = 9.008(6) Å, b = 28.690(15) Å, c = 14.528(7) Å, a = 90 degrees, beta = 104.12(7) degrees, gamma = 90 degrees, Z = 8, R = 0.0695.

Journal Article↗