Polyfunctional fluoroalkyl-containing carbonyl compounds in the synthesis of heterocycles

Efficient procedures for the regioselective synthesis of fluoroalkyl-containing threefive-, six-, and seven-membered heterocycles as well as of related fused compounds, namely, α,β-epoxyketones, α,β-aziridinylketones, pyrazoles, pyrazolines, isoxazolines, 1,2-dithiolenes, amino- and mercaptopyrimidines, Δ^3,5-2-thioxo-1,3,2-thiazaphosphorines, Δ^3,5-2-thioxo-1,3,2-oxazaphosphorines, 2,3-dihydro-1,4-diazepines, azirino[1,2-a]quinoxalines, benzo[b]-and naphtho[2,3-b]-1,4-diazepines, and triazolopyridazines, which have been developed by the authors and coworkers, are summarized. The α- and β-functionalized fluoroalkylcontaining carbonyl compounds (β-diketones, β-ketoesters, their salts, regioisomeric β-aminovinyl ketones, β-aminovinylthiones, β-hydroxyketones, α,β-enones, and their halogen derivatives) were used as synthons in the processes of formation of the above-mentioned heterocycles. Dedicated to the memory of Academician I. Ya. Postovskii on his 100th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1279–1286, July, 1998.     

Preparative synthesis of the Corey chiral controller for enantioselective dihydroxylation of olefins

A five-step synthesis of both enantiomers of 1,2-di(2,4,6-trimethylbenzylamino)-1,2-diphenylethane,i.e., Corey (R,R)- and (S,S)-controllers for enantioselective dihydroxylation of olefins by osmium tetroxide, starting from α,α′-diphenylglyoxime, has been developed. The key operations in the synthesis are the optical resolution of intermediaterac-1,2-diamino-1,2-diphenylethane into two enantiomers using only (R,R)-tartaric acid and the subsequent enhancement of the enantiomeric purity to >98% by crystallizations of the corresponding Schiff's bis-bases. Analysis of the enantiomeric purity of the controllers can be easily performed using¹H NMR spectra of their salts with (R)-α-methoxy-α-(trifluoromethyl)phenylacetic acid (MosherR-acid). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 101–105, January, 1997.     

Theoretical study on structures and stability of HC2P isomers

 The structures and isomerization pathways of various HC₂P isomers in both singlet and triplet states are investigated at the B3LYP/6-311G(d,p), QCISD/6-311G(d,p) (for isomers only) and single-point CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) levels. At the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level, the lowest-lying isomer is a linear HCCP structure ³ 1 in the ³∑⁻ state. The second low-lying isomer has a CPC ring with exocyclic CH bonding ¹ 5 in a singlet state at 10.5 kcal/mol. The following third and fourth low-lying isomers are a singlet bent HCCP structure ¹ 1 at 20.9 kcal/mol and a bent singlet HPCC structure ¹ 3 at 35.8 kcal/mol, respectively. Investigation of the HC₂P potential-energy surface indicates that in addition to the experimentally known isomer ³ 1, the other isomers ¹ 1, ¹ 3 and ¹ 5 also have considerable kinetic stability and may thus be observable. However, the singlet and triplet bent isomers HCPC ¹ 2 and ³ 2 as well as the triplet bent isomer HPCC ³ 3 are not only high-lying but are also kinetically unstable, in sharp contrast to the situation of the analogous HCNC and HNCC species that are both kinetically stable and that have been observed experimentally. Furthermore, the reactivity of various HC₂P isomers towards oxygen atoms is briefly discussed. The results presented here may be useful for future identification of the completely unknown yet kinetically stable HC₂P isomers ¹ 1, ¹ 3 and ¹ 5 either in the laboratory or in interstellar space. Received: 5 November 2000 / Accepted: 25 November 2001 / Published online: 8 April 2002     

Theoretical predictions of the structure, gas-phase acidity and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid

Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure, acidity (free energy of deprotonation, ΔG^o), and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid (3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone, H₂C₄Se₂S₂) are reported. The global minimum found on the potential energy surface of 1,2-diseleno-3,4-dithiosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutenedithiol. The computed aromatic stabilization energy (ASE) by homodesmotic reaction (Eq 1) is −20.1 kcal/mol (MP2(fu)/6-311+G** //RHF/6-311+G**) and −14.9 kcal/mol (B3LYP//6-311+G**//B3LYP/6-311+G**). The aromaticity of 1,2-diseleno-3,4-dithiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (Λ) −17.91 (CSGT(IGAIM)-RHF/6-311+G**//RHF/6-311+G**) and −31.01 (CSGT(IGAIM)-B3LYP/6-311+G**//B3LYP/6-311+G**). Thus, 1,2-diseleno-3,4-dithiosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated theoretical gas-phase acidity is ΔG^o _1(298K)=302.7 kcal/mol and ΔG^o _2(298K)=388.4 kcal/mol. Hence, 1,2-diseleno-3,4-dithiosquaric acid is a stronger acid than squaric acid(3,4-dihydroxy-3-cyclobutene-1,2-dione, H₂C₄O₄). Received: 11 April 2000 / Accepted: 7 July 2000 / Published online: 27 September 2000     

Endohedral chemical shifts in higher fullerenes with 72–86 carbon atoms

For all isolated pentagon isomers of the fullerenes C₆₀–C₈₆ with nonzero HOMO–LUMO gap and for one nonclassical C₇₂ isomer (C_{2 v} ), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The experimental ³He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C₆₀, C₇₀ and C₇₆). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental ³He chemical shifts, the assignments of the observed ³He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C₈₂ and one C₈₆ isomer (C₈₂:3 and C₈₆:17). The calculated helium chemical shifts also suggest the reassignment of the δ(³He) resonances of two C₇₈ isomers. Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001     

Interaction of polynitro compounds with difluoroamine

Difluoroamine does not react with tetranitromethane and fluoro-, chloro-, and bromotrinitromethanes in DMF and in acidic media (CF₃COOH, ClSO₃H, FSO₃H, and oleum), but reacts with α-fluoro- and α-(difluoroamino)-α,α-dinitrotoluenes to give substitution products of the difluoroamino group for both the nitro groups,viz., PhC(NF₂)₂F and PhC(NF₂)₃, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1647–1649, August, 1998.     

Intercalation of 1,2-Alkanediols into α-Zirconium Hydrogenphosphate

Intercalation compounds of α-Zr(HPO₄)₂ · H₂O with 1,2-alkanediols (from C3 to C16) have been prepared by replacing 1-propanol in α-Zr(HPO₄)₂ · 2C₃H₇OH with the desired 1,2-alkanediols by a treatment in a microwave field. It was found that the intercalates contain 1.5 molecules of diol per formula unit. The diol molecules are placed between the host layers in a bimolecular way with their aliphatic chains tilted at an angle of 51°. The diol molecules are anchored in the interlayer space by H-bonds. A mixed intercalate, containing 1,2-butanediol and 1,2-decanediol in a roughly equimolar ratio, is formed when the α-Zr(HPO₄)₂ · 2C₃H₇OH intercalate, suspended in a mixture of 1,2-butanediol and 1,2-decanediol, is exposed to microwave radiation. No new phase containing both types of the guest molecules was observed when the 1-propanol intercalate, suspended in a mixture of 1-propanol and 1,2-octanediol, is exposed to microwave radiation.     

Theoretical study of the potential-energy surface of C2NP

 The B3LYP/6-311G(d) and CCSD(T)/6-311G(2df) (single-point) methods have been used to investigate the singlet potential energy surface of C₂NP, in which seven stationary isomers and seventeen interconversion transition states are involved. At the final CCSD(T)/6-311G(2df)//B3LYP6-311G(d) level with zero-point vibrational energy correction the lowest-lying isomer is a linear NCCP followed by two linear CNCP isomers at 23.9  and CCNP at 65.8 kcal mol⁻¹, respectively. The three isomers are kinetically very stable towards both isomerization and dissociation, and CCNP is even more kinetically stable than CNCP – by 14.3 kcal mol⁻¹ despite its high energy. Further comparative calculations were performed at the QCISD and QCISD(T) levels with the 6-311G(d) and 6-311G(2d) basis sets to obtain more reliable structures and spectroscopy for the three isomers. The calculated bond lengths, rotational constant, and dipole moment for NCCP were in close agreement with the experimentally determined values. Finally, similarities and discrepancies between the potential energy surface of C₂NP and those of the analogous species C₂N₂ and C₂P₂ were compared. The results presented in this paper might be helpful for future identification of the two still unknown yet kinetically very stable isomers CNCP and CCNP, both in the laboratory and in interstellar space. Received: 3 January 2001 / Accepted: 6 June 2001 / Published online: 30 October 2001     

The structure and CH-acidity of CF3-substituted β-thiolactones. A theoretical study

Ab initio calculations of the molecules of CH₃- and CF₃-substituted β-propiothiolactones and the productsof their deprotonation were carried out by the restricted Hartree—Fock method with full geometry optimization using the 6–31 G^* basis set. Peculiarities of the geometry and electronic structure of the systems in question were established. Only 2-methyl-β-propiothiolactone forms a mesomeric stabilized carbanion in the case of proton abstraction from the α-position of thiolactone cycle. Carbanions of 3-methyl, 2-, and 3-thrifluoromethyl-β-propiothiolactones are stabilized due to the ring opening to form ketene thiolate ions. The CH-acidity of fluorine-containing β-thiolactones is much higher than that of nonfluorinated analogs (the differences in the deprotonation energies are 13.4 to 25.2 kcal mol⁻¹). Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1719–1725, September, 1998.