NMR study of the effect of nitrogen-borane coordination on the conformational equilibrium of six membered ring heterocycles.

Flores‐Parra, Angelina; Farfán, Norberto; Hernandez‐Bautista, A. I.; Fernández-Sánchez, Lilia; Contreras, Rosalinda

doi:10.1016/s0040-4020(01)96146-0

Cited by 46 publications

(8 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The strong intramolecular hydrogen bonds O-H···N of compounds 1-3 15 are indicative that in the corresponding boron or gallium esters, these atoms would occupy the place of the proton, Scheme 2. This idea is supported by the report that diphenyl borinic esters of 4-hydroxypiperidine 7 and 1,4-diethanolpiperazine 24 present strong intramolecular N→B coordination leading to spiro-compounds.…”

Section: -13mentioning

confidence: 72%

“…From the NMR experiments the N→B coordination bond energy of 10-11 was calculated and the values are 50.8 (10) and 55.7 kJ mol -1 (11); these are higher than those found for the free ligands 1 and 2 (45.4 and 49.3 kJ mol -1 ) 15 and N-methyl-dithiazinane (46 kJ mol -1 ), 16,21 however they are weak bonds in the range found for N→B heterocycles (50 -81 kJ mol -1 ). A view of compounds 5 and 9 in the C7-C8 bond axis (left in Figures 3 and 4) shows the preferred envelope conformation of the five membered ring, with the nitrogen atom out of the ring plane, and that the phenyl or methyl group is in the equatorial position.…”

Section: Methodsmentioning

confidence: 90%

“…They are used as flavouring agents 1 catalysts, 2 antibiotics 2,3 or reagents in organic synthesis. 4,5 The coordinating ability of the simple dithiazinanes was already tested using BX 3 reagents (X = H or halogen), in all cases the nitrogen is the more basic site, [6][7][8][9][10][11][12][13] …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Boron and gallium esters derived from 2-(1,3,5-dithiazinan-5-yl)-ethanols

Gálvez-Ruíz¹,

Solano-Ruiz²,

Sánchez-Ruíz³

et al. 2007

Arkivoc

Self Cite

View full text Add to dashboard Cite

Compounds 2-(1,3,5-dithiazinan-5-yl)ethanol (1), 2-methyl-2-(1,3,5-dithiazinan-5-yl)ethanol (2) and 2-phenyl-2-(1,3,5-dithiazinan-5-yl)ethanol (3) reacted with BF 3 ⋅OEt 2 and BCl 3 ⋅DMS, 1 and 2 with (Ph 2 B)O, and 2 and 3 with GaCl 3 giving the corresponding chelates, bearing N→BF 2 O, N→BCl 2 O N→BPh 2 O, and N→GaCl 2 O groups. The internal coordination N→M (M = B or Ga) afforded spiro-compounds, where nitrogen is the central atom. Compounds were mainly characterized by 11 B, 1 H and 13 C NMR. The N→B or N→Ga coordination bond was detected in the 1 H spectra because coordination stops the ring inversion of the dithiazinane ring differentiating equatorial and axial protons. The presence of a sterogenic center at the ethanol arm (ligands 2 and 3), differentiates C4H 2 and C6H 2 upon coordination. Minimum energy structures for boron compounds were calculated [ab initio 6-31G(d,p)]. VT NMR experiments for diphenyl borinic esters were performed in order to estimate the N→BPh 2 coordination energy. X-ray diffraction analyses of the hydrochloride of ligand 1 and of the gallium compound prepared from 2 were obtained.

show abstract

Section: -13mentioning

confidence: 72%

Section: Methodsmentioning

confidence: 90%

See 1 more Smart Citation

Boron and gallium esters derived from 2-(1,3,5-dithiazinan-5-yl)-ethanols

Gálvez-Ruíz¹,

Solano-Ruiz²,

Sánchez-Ruíz³

et al. 2007

Arkivoc

Self Cite

View full text Add to dashboard Cite

show abstract

“…In contrast, reaction of ephedrine with glyoxal, under the same reaction conditions, affords a mixture of (2R*,3S*, 6R* ,7S*) -2,6 -diphenyl-3,4,7,8 -tetramethyl-cis-perhydro- [ (8) and (5S* ,6R*)-4,5-dimethyl-6-phenyl-l,4-oxazin-2-one (9) (9).…”

Section: Resultsmentioning

confidence: 99%

Fused heterocycles derived from pseudoephedrine and ephedrine

Farfán¹,

Santillán²,

Castillo³

et al. 1992

Can. J. Chem.

Self Cite

View full text Add to dashboard Cite

). The formation of heterobicycles by condensation of (IR, 2R)-(-)-pseudoephedrine or (lR, 2s)-(-)-ephedrine with glyoxal is reported. In the case of pseudoephedrine, the nuclear magnetic resonance data of the crude reaction mixture indicate the presence of three isomeric compounds (5, 6, and 7), which were separated by fractional crystallization, while ephedrine afforded the oxazino-oxazine 8 and the known (5S*,6R*)-4,5-dimethyl-6-phenyl-1,4-oxazin-2-one (9). Conclusive spectroscopic evidence for the structures of the new compounds having the cis-[1,4]oxazino[3,2-b]-1,4-oxazine (5 and 8) and the 2,2'-bioxazolidine type structures (6 and 7) was obtained by measurement of the I3c satellite coupling constants in the 300 MHz 'H nmr spectra, combined with the evaluation of dihedral angles using a modified Karplus type relationship. Unequivocal 'H and I3c nmr spectral assignments for all new compounds were done using two-dimensional carbon-proton correlation experiments. Syntheses of the known 5a,6,1la,l2-tetrahydro[l,4]benzoxazino[3,2-blbenzoxazine (3a) whose crystal structure has been previously determined, as well as of its N,Nf-diisopropyl derivative 36, allowed us to corroborate the above observations for the six-membered ring heterocycles. Moreover, the structures of 36 and 7 were independently verified by single crystal X-ray diffraction studies, thus validating the structural conclusions deduced from nmr satellite multiplicity measurements.

show abstract

“…Extensive work has been published on the nature of the B--N bond [1], mainly for amines and borane as a Lewis system in tetrahydrofuran (THF) as solvent, and from chemical, conformational, and spectroscopic points of view [2]. However, very few thermochemical studies have been reported for this kind of compounds.…”

Section: Introductionmentioning

confidence: 99%

Thermochemistry of amineborane adduct formation of pyridine and picoline isomers

Flores

Torres

1996

Struct Chem

View full text Add to dashboard Cite

The enthalpy of reaction of pyridine, 2-, 3-, and 4-picoline with BH3.THF and the enthalpy of solution of the same amines in THF were determined by reaction-solution calorimetry. From these data, the enthalpies of formation of the corresponding amineborane adducts in solution of THF were also determined. The results can be explained by considering the steric and inductive effects of the methyl group on the pyridine ring and the basicity of amines. The enthalpy of formation of the adducts in solution of THF correlates well with the available literature values of pK,, of amines also determined in THF, and the influence of the solvent on the basicity features of studied amines is verified.

show abstract

NMR study of the effect of nitrogen-borane coordination on the conformational equilibrium of six membered ring heterocycles.

Cited by 46 publications

References 15 publications

Boron and gallium esters derived from 2-(1,3,5-dithiazinan-5-yl)-ethanols

Boron and gallium esters derived from 2-(1,3,5-dithiazinan-5-yl)-ethanols

Fused heterocycles derived from pseudoephedrine and ephedrine

Thermochemistry of amineborane adduct formation of pyridine and picoline isomers

Contact Info

Product

Resources

About