Hugo Tlahuext

Chlorination reactions of ephedrines revisited. Stereochemistry and functional groups effect on the reaction mechanisms

The stereochemistry of the chlorination reactions with SOCl2 of free ephedrine and pseudoephedrine and their hydrochlorides, oxamides and sulfonamides was analyzed. Chlorination of free and hydrochloride erythro isomers occurs with 100% inversion of configuration at C-1 (S N2 mechanism). Chlorination of oxamides and sulfonamides of erythro isomers occurs with retention of the configuration at C-1, (S Ni mechanism). Chlorination reactions in all threo isomers and derivatives hydrochlorides, oxamides or sulfonamides gave the same ratio of erythro (40%) and threo isomers (60%) (SN1 mechanism). Treatment of the isomeric mixture of the chlorodeoxyephedrine and chlorodeoxypseudoephedrine hydrochloride in DMSO with HCl changes the isomeric ratio, increasing the erythro isomer content (65%). Using the erythro ethanolamines it is possible to arrive stereoselectively at the erythro chloroamines if the compound is previously tosylated or converted to the amide, or to the threo chloroamines if the compound is directly chlorinated with SOCl2.

Versatile behavior of 2‐guanidinobenzimidazole nitrogen atoms toward protonation, coordination and methylation

The structure, dynamic behavior, protonation, methylation, and coordination sites of 2-guanidinobenzimidazole la were investigated. Structures of compounds [2-guanidinium-1,3,10-trihydrobenzimidazole]sulfate lb, [2-guanidinium-l,3-dihydro-benzimidazole]sulfate lc-ld, [2-guanidinium-l,3-dihydro-benzimidazole]tetrafluoroborate le, [2-guanidinium-l,3-dihydro-benzimidazole]chbride If, [2-guanidinium-1,3dihydro-benzimidazole] perchlorate 1% 2-guanidinoI-methyl-benzimidazole 2a, [2-guanidinium-l,3-dimethyl-benzimidazole]iodide 2b, [2-guanidinium-1methyl-3-hydro-benzimidazole]chloride 2c, [2

1 H, 13C, 15N, 2D and variable temperature NMR study of the role of hydrogen bonding in the structure and conformation of oxamide derivatives

The structure and conformation of N,N′-bis[(2-hydroxy)phenyl]oxamide (1); N,N′-bis[(2-methoxy)-phenyl]oxamide (2); N,N′-bis(phenyl)oxamide (3); N,N′-bis[(1R,2S)-(–)-norephedrine]oxamide (4); N,N′-bis[(1R,2R)-(–)-norpseudoephedrine]oxamide (5); N-[(2-hydroxy)phenyl]methylamide (6); N-[(2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[(–)-norephedrine]-methylamide (9) and N-[(–)-norpseudoephedrine]methylamide (10) were unambiguously established by 1H, 13C, 15N, 2D and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1–5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1, 2, 4 and 5 present the amidic proton coordinated by two oxygen atoms.

Synthesis of optically active boroxazolidine, borathiazolidine and boraselenazolidine and their N-borane adducts from the corresponding 2-imino-heteroazolidines

Abstract The synthesis from the corresponding 2-imino-heteroazolidines of optically active boroxazolidine, borathiazolidine and boraselenazolidine, derived from ephedrine, and their N-borane adducts is reported. The X-ray diffraction structures of (4R,5R)-(+)-3,4-dimethyl-5-phenyl-2-iminium thiazolidine thiocyanate 9b, (4R,5R)-(+)-3,4-dimethyl-5-phenyl-2-iminium-selenazolidine selenocyanate 9c, (4R,5R)-(+)-3,4-dimethyl-5-phenyl-2-iminoselenazolidine 10b and (4R,5R)-(+)-3,4-dimethyl-5-phenyl-2-boraselenazolidine dimer 15 were elucidated. Compounds were also studied by 1H, 13C and 77Se NMR.

N-alkyloxazaborolidines derived from ephedrines.

Abstract The synthesis of oxazaborolidines from amides derived from ephedrine and pseudoephedrine by treatment with BH3-THF is reported. The reaction affords chiral oxazaborolidines with nitrogen atom substituents of different steric requirements enlarging the potential of new oxazaborolidines prepared from readily available ephedrines. These may be useful in asymmetric synthesis.

Diborane derivatives from N-alkyloxazaborolidines

Abstract N-methyl or N-ethyl oxazaborolidines derived from ephedrines react with B2H6 to afford N-BH3 adducts. N-methyl derivatives dimerize. Monomers and dimers can be considered as diborane derivatives. Borane addition was found to be stereoselective for 8 and 10.

Boron Heterocycles Derived from 2- Guanidinobenzimidazole

The syntheses and structure determinations of a series of boron heterocycles derived from 2-guanidinobenzimidazole 1 are reported. Structures of new compounds, 2-guanidino-1-methyl-benzimidazole 2, diphenyl-(2-guanidinobenzimidazole-N,N′)-borate 3, diphenyl-(2-guanidino-1-methyl-benzimidazole-N,N′)borate 4, hydroxy-phenyl-(2-guanidino-benzimidazole-N,N′)borate 5, hydroxy-phenyl-(2-guanidino-1-methyl-benzimidazole-N,N′)borate 6,methoxy-phenyl-(2-guanidinobenzimidazole-N,N′)borate 7, isopropoxy-phenyl-(2-guanidinobenzimidazole-N,N′)borate 8, acetoxy-phenyl-(2-guanidinobenzimidazole-N,N′)borate 9, methoxy-phenyl-(2-guanidino-1-methyl-benzimidazole-N,N′)borate 10, dihy-droxy-(2-guanidino-1-methyl-benzimidazole-N,N′)borate 16, difluoro-(2-guanidinobenzimidazole-N,N′)borate, 17, dihydroxy-(2-guanidino-1-benzimidazole-N,N′)borate potassium salt 19, diphenyl-(2-guanidinium-10H-benzimidazole-N,N′)borate hydro-chloride 20, methoxy-phenyl-(2-guanidinobenzimidazole-N,N′)borate hydrochloride 21, and N10-borane-(diphenyl-2-guanidinobenzimidazole-N,N′)borate 22, were determined based on 1H, 13C, 15N, and 11B spectroscopy. The X-ray diffraction structures of 3–7, 19, and 20 were obtained. The formation of N3-borane adducts 11 and 12 derived from compounds 1 and 2, respectively, and the dihydride-(2-guanidinobenzimidazole-N,N′)borate 13 and dihydride-(2-guanidino-1-methyl-benzimidazole-N,N′)borate 14 were observed by 11B NMR. The results show that 2-guanidinobenzimidazole gives stable borate heterocycles with a delocalized π electronic system. A dynamic exchange of N–H protons was observed with preferred protonation at N-12. The new heterocycles are protonated at N-10 by acidic substances to give pyridinium-type heterocycles or can lose a proton to give iminium salts.

Determination of the nitrogen configuration in ephedrine N-boranes and a study of their assisted stereospecific deuteration of NH

Abstract Ephedrine, pseudoephedrine and pseudoephedrine-methyl-ether react stereoselectively with BH3.DMS to give N→BH3 adducts, which are N-epimers of stable configuration. The nitrogen configuration was established from NMR data. Assisted stereospecific deuteration of OH was demonstrated by comparison with the behaviour of pseudoephedrine-methyl-ether N-BH3 adducts. The analysis of the preferred conformers gave us an explanation of the observed stereochemistry.

Application of 11B NMR spectroscopy to the study of the reactivity of ortho substituted anilines with BH3•THF. I: Formation reactions of new boron heterocycles

Abstract The existence of various intermediates in the formation of some boron heterocycles was revealed by 11 B NMR spectroscopy. The structure of these intermediates was established by comparing them with model compounds. Four new boron heterocycle compounds bearing a hydride function and three new spiroborates with catechol and ortho substituted anilines as ligands were prepared. The structures were established by spectroscopic measurements.

Do spiroarsoranes exhibit polytopal equilibrium in solution

The spiroarsoranes 5-phenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (6), (3R,8R)-3,8-dimethyl-5-phenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (7), (2S,7S)-2,7-dimethyl-5-phenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (8), and (3S,8S)-3,8-dimethyl-(2R,7R)-2,5,7-triphenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (9) were prepared by reaction of phenylarsonic acid and the correspondig amino alcohol. The presence of polytopal Delta left arrow over right arrow Lambda equilibrium in 6-9 was demonstrated by HPLC and NMR studies. NBO computations at the MP2/6-31+G(2d,2p) level indicate that methyl substitution in C2 or C3 of the oxazarsolane ring determines the predominance of Delta or Lambda stereoisomers. GIAO B3LYP/6-311++G(2d,2p) computations were used to assign experimental (1)H and (13)C NMR spectra.