Tetraaryl-1,3-dioxolane-4,5-dimethanols as catalysts for the addition of trimethylsilyl cyanide to benzaldehyde and the oxirane ring

The synthesis of 1,2-, 1,3-, and 1,4-phenylene-bis[(4R,5R)-4,5-di(hydroxydiphenylmethyl)-1,3-dioxolane]s (ortho-, meta-, and para-bis-(R,R)-TADDOLs) and bis[4-{[(4R, 5R)-4,5-di(hydroxydiphenylmethyl)]-1,3-dioxolan-2-yl}phenyl]methane was carried out. The possibilities of the use of these compounds as catalysts for the C-C bond formation in the addition of Me₃SiCN to benzaldehyde and the oxirane ring opening in cyclohexene oxide by Me₃SiCN were investigated. The catalytic activity of different bis-(R, R)-TADDOLs in this series depends on their structure. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1451–1458, August, 2007.     

Heteroorganic betaines. 8. Synthesis and structures of silicon- and germanium-containing organoarsenic betaines R13As+—CR2R3—EMe2—S– (E = Si,Ge)

The reactions of ylides R¹ ₃As=CHR² with hexamethyl-2,4,6-trisila- and hexamethyl-2,4,6-trigermatrithiacyclohexanes afforded betaines R¹ ₃As⁺—CHR²—SiMe₂—S^– (2) (R¹ = Et; R² = Ph (a), Me₃Si (b); R¹ = R² = Ph (c)) and Et₃As⁺—CH(SiMe₃)—GeMe₂—S^– (3), respectively. Betaines 2a,b and 3 were characterized by multinuclear NMR spectroscopy. According to the X-ray diffraction data, in the crystals the As⁺—C—E—S^– main chain (E = Si or Ge) of molecules 2a,b and 3 adopts a twisted cis conformation due to strong intramolecular Coulomb interactions between the anionic and cationic centers. The equilibrium geometries of isolated molecules 2a and 3, which were calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set), are in qualitative agreement with the X-ray data. In solutions, betaines 2a (in the absence of Li salts) and 2c (in the presence of LiBr) selectively decomposed according to the Corey—Chaykovsky reaction, which was accompanied by elimination of R₃As and, probably, the intermediate formation of silathiirane. The subsequent transformation of the latter afforded 2,2,4,4-tetramethyl-5-phenyl-2,4-disila-1,3-dithiolane.     

Catalytic Asymmetric Synthesis of O‐Acetylcyanohydrins from Potassium Cyanide,Acetic Anhydride,and Aldehydes,Promoted by Chiral Salen Complexes of Titanium(IV) and Vanadium(V)

The utility of the chiral [Ti(μ‐O)(salen)]₂ complexes (R)‐ and (S)‐ 1 (H₂salen was prepared from (R,R)‐ or (S,S)‐cyclohexane‐1,2‐diamine and 3,5‐di(tert‐butyl)‐2‐hydroxybenzaldehyde) as catalysts for the asymmetric addition of KCN and Ac₂O to aldehydes to produce O‐acetylcyanohydrins was investigated. It was shown that the complexes were active at a substrate/catalyst ratio of 100 : 1 and produced the O‐protected cyanohydrins with ee in the range of 60–92% at −40°. Other complexes, [Ti₂(AcO)₂(μ‐O)(salen)₂] ((R)‐ 4 ) and [Ti(CF₃COO)₂(salen)] ((R)‐ 5 ), were prepared from (R)‐ 1 by treatment with different amounts of Ac₂O and (CF₃CO)₂O, and their catalytic activities were tested under the same conditions. The efficiency of (R)‐ 4 was found to be even greater than that of (R)‐ 1 , whereas (R)‐ 5 was inactive. The synthesis of the corresponding salen complexes of V^IV and V^V, [V(O)(salen)] ((R)‐ 2 ) and [V(O)(salen)(H₂O)] [S(O)₃OEt] ((R)‐ 3 ), was elaborated, and their X‐ray crystal structures were determined. The efficiency of (R)‐ 3 was sufficient to produce O‐acetyl derivatives of aromatic cyanohydrins with ee in the range of 80–91% at −40°.     

The nature of the O—O bond in hydroperoxides

Quantum-chemical calculations of the H₂O₂ and F₂ molecules using different computational schemes, basis sets, and procedures for the inclusion of electron correlation were performed. High-resolution X-ray diffraction study of the electron density distribution in the crystals of 2,5-dimethyl-2,5-dihydroperoxyhexane and 2,5-dimethyl-2,5-dihydroperoxyhex-3-yne was carried out. Joint analysis of the results obtained showed that the formally covalent O—O and F—F bonds correspond to a specific type of interatomic interaction. This type is intermediate between the shared and closed-shell interactions (the latter are typical of the ionic systems and van der Waals molecules).     

Reaction of perfluoro-2-methyl-2-pentene with cycloalkanone oximes: new examples of the Beckmann—Chapman rearrangement

The base-catalyzed reaction of cycloalkanone oximes (la,b) with perfluoro-2-methyl-2-pentene (PFMP) initially affords the addition products,i.e., fluoroalkyl ethers (2a,b). In the presence of KOH, the latter undergoes dehydrofluorination to give perfluoroalkenyl ethers (3a,b). Thermolysis of ethers3a,b results in compounds of two types — pyrrolines (4a,b) andN-perfluoroalkenyl lactams (5a,b). The latter are also prepared from PFMP and the corresponding lactams. The structure ofN-[perfluoro-(2-methyl-2-penten-3-yl)]-2-pyrrolidone (5c) was established by X-ray diffraction study.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1073–1077, June, 1994.     

X-ray structural study of 2-amino-5,5-dimethoxy-3-cyano-4-dicyanomethylene-4,5-dihydropyrrole and its sodium salt

According to the XSA data, a conjugation system in which both endo- and exocyclic bonds are included is realized in the molecule of 2-amino-5,5-dimethoxy-3-cyano-4-dicyanomethylene-4,5-dihydropyrrole and the anion of its sodium salt due to the planar structure, and this is reflected in their unusual length. Due to the developed system of intermolecular hydrogen bonds, the molecules in the crystals are joined in infinite three-dimensional motifs.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, Moscow 117813, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 510–517, April, 1998.