Stereoselectivity of additions to N-methyl acetonitrilium fluorosulfonate.

Alkoxy-N-methyl-acetiminium salts were prepared by addition of CH3OH and C2H5OH to N-methyl acetonitrilium fluorosulfonate at low temperature. Analysis of the 5J(HH) and 3J(13C–H) coupling constants in the NMR spectra showed an anti addition with a diastereoselectivity of >95%. Deprotonation of these salts with (Z)-configuration gave the corresponding N-methyl-alkoxyacetimines with very high (E)-configuration.

cis,trans,cis,cis-7-tert-Butyl-dimethyl-silyl-oxy-4,10-dimethyl-tetra-cyclo[5.4.1.0.0]dodecan-2-one.

In the structure of the title compound, C(20)H(34)O(2)Si, a cis,trans,cis,cis-[4.5.5.

(RSS)-[N-Hydroxyethyloxy]-hexafluoroVal-MeLeu-Ala tert-butyl ester.

THE TITLE COMPOUND [SYSTEMATIC NAME: (2S,5S,8R)-tert-butyl 8-(1,1,1,3,3,3-hexafluoropropan-2-yl)-12-hydroxy-5-isobutyl-2,6-dimethyl-4,7-dioxo-10-oxa-3,6,9-triazadodecanoate], C(21)H(36)F(6)N(3)O(6), is a tripeptide crystallizing in the chiral ortho-rhom-bic spacegroup P2(1)2(1)2(1). The absolute configuration (R) of the chiral center in the hexa-fluoro-valine unit is based on the known stereochemistry of MeLeu and Ala (SS). The N-hydroxy-ethyl-oxy substituent of hexa-fluoro-valine is positionally disordered [occupancy ratio 0.

Model studies for the thiol-mediated methyl transfer to corrinoids.

The thiol-dependent methylation of heptamethyl cob(II)yrinate 8r with methyl iodide and methyl tosylate was explored under a variety of conditions. The interaction of the heptamethyl cob(II)yrinate with a variety of thiols was monitored prior to the addition of the methylating agent, and the formation of the Co(I) complex was only apparent in the reaction with hexane thiol. Nevertheless, thiol-mediated methylation of the Co(II) complex 8r takes place with methyl iodide under most conditions.