Macrocycle methylated

The CO2 binding constants of the corresponding [CoHMD]+ isomers are quite different N-rac-[CoHMD], (1.2 0.5) x 10 M A - evo-[CoHMD]+, 165 15 M l [5,6]. While hydrogen bonding interactions between the bound CO2 and amine protons of the macrocycle will tend to stabilize both adducts, the N-meso adduct is destabilized by the steric repulsion by the macrocycle methyl group. 

Oxidation of /U-cresol afforded a triphenol 22 which is approximately half the molecule. The central hydroxyl of the triphenol could be selectively methylated and then the compound was ort/ro-brominated and bridged using 1,3-dibromopropane to give 23. Metallation with butyllithium followed by iron catalyzed coupling afforded the macrocycle as indicated. 

The corphins 2 and 3 formed can be tautomerized back to pyrrocorphins,6 but less complicated model compounds bearing methyl groups can also be similarly tautomerized.yab When magnesium nonamethylpyrrocorphin is first methylated and then tautomerized, the D pyrrole ring is regioselectively attacked by iodomethane followed by tautomerization to establish a pyrrole ring in the C position of the macrocyclic system 4. 

By reaction of 2-alkyl-4,6-dichloro-l,3,5-trimethylborazines (alkyl = methyl, ethyl, i-propyl) with bis(trimethylsilyl)amine the tetrameric borazine ring systems 4-6 are produced (Fig. 2) they can be purified by several successive vacuum sublimations (yields 4-60%). If the borazines carry n-propyl and tert-butyl groups in the 2-position or if methylbis(trimethylsilyl)amine is used to bridge the borazine molecules, the macrocyclic ring formation is inhibited [17, 18]. 

Fig. 2-1 Proposed structures of three macrocyclic glycopeptides. On teicoplanin, R = 8-methyl-nonanoic acid.

Imines, either acyclic or macrocyclic but invariably multidentate, have a rich coordination chemistry that has been investigated at length. The 7r-accepting ability of imine donors results in the stabilization of lower oxidation states relative to their saturated amine analogs, and there exist many air-stable divalent imine complexes of Co, in contrast to amine relatives. The hexa-methyl-diene (52) has been the most intensively studied ligand of this class, particularly when complexed with Co. In addition, Co complexes of the dimethyl (53),295,296 tetramethyl (54),297 pentamethyl (55)298 and octamethyl (56)299 macrocyclic dienes are also known. In the presence of... 

Methylation of [Co(tmt)]2+ with Mel leads to the potent methyl carbanion donor trans-[Co(tmt)Me2]+ (186). Reaction of this complex with variety of methyl-lead(IV) compounds in MeCN is rapid, leading to the same monomethylcobalt(III) product, but resulting in different methylated Pb derivatives depending on the reaction stoichiometry and Pb compound.839 The same complex rapidly transfers Me groups to Zn2+ and Cd2+ in MeCN,840 or Pb2+ and Sn2+ in water.302,841 The kinetics of Co—C bond formation in the reactions with primary alkyl and substituted primary alkyl radicals has been found to be influenced more by the structure of the macrocycle than by the nature of the radicals.842... 

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