Enantiomers of polarized alkenes: chromatographic enrichment and thermal interconversion

(+)- and (?)-$\text{1}$ as well as (+)- and (?)-$\text{2}$ were partially separated by liquid chromatography on triacetylcellulose; racemizations resulted in the barriers (Table 2) to rotation via planarized transition states.     

Enantiomers and barriers to racemization of sterically hindered N-aryl- and N-heteroarylpyrroles

The N-aryl- and N-heteroaryl-2,5-dimethylpyrrole-3-carbaldehydes 2–8 have been synthesized by condensation of hexane-2,5-dione with the appropriate amine and subsequent Vilsmeier-Haack formylation of the pyrrole ring. Diastereomeric association complexes of the racemic pyrrole 8 were studied by pmr chemical shifts and the splittings induced by (+)-1-(9-anthryl)-2,2,2-trifluoroethanol. Enrichment of the enantiomers M and P of 2 and 6 was achieved by liquid chromatography on triacethylcellulose. The barrier to partial rotation about the C-N bond in 6 was determined by thermal racemization and its lower limits in 2 and 8 were estimated.     

Syntheses of extreme sterically hindered 4-methoxyboronic acids

4-Iodoanisoles 3a,b, 3d and 4-bromoanisoles 4a-d were readily obtained. An extreme steric hindrance precluded obtaining 3c. Catalytic borylation of 3a,b, 3d followed by hydrolysis of boronic ester 26a,b, 26d easily provided the boronic acids 5a,b, 5d. Compounds 5a and 5d were also synthesised, starting from 4a and 4d, by halogen/metal exchange. Because of a too important steric hindrance, this last reaction failed with 4c and 4b led to the unexpected but stable boronic ester 6. The final obtaining of 5b required a strongly basic hydrolysis with heating.     

Utilizing o-quinone methide chemistry: synthesis of sterically hindered acridin-4-ols

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High-pressure transesterification of sterically hindered esters

A mild, rapid, and efficient method for the solvolysis of sterically hindered esters under high pressure is described. Transesterification is carried out in the presence of DBU at room temperature and at a pressure of 10 kbar to give quantitative conversions within short reaction times. The substrates examined included aromatic and aliphatic esters of sterically hindered alcohols and phenols. An optically pure benzyl ester of phenylalanine was chosen to study racemization of the amino acid esters under high-pressure reaction conditions.     

Self-addition of a sterically hindered alkynylselenolate

[structure: see text] The unprecedented formation of a complex macrocyclic selenium-carbon ring system, which is initiated by the action of coordinating reagents upon a sterically hindered alkynylselenolate, has been observed. The crystal structure of the product could be obtained and shows a rigid tricyclic arrangement consisting only of selenium and sp(2)-hybridized carbon atoms. This reactivity stands in contrast to the corresponding unsubstituted alkynylselenolates and is an example where a bulky substituent destabilizes an adjacent unsaturated pi-system.     

Aquametric microdetermination of sterically hindered ketones

Conclusions The previously developed aquametric micromethod for determining carbonyl compounds also gives reliable results when most of the sterically hindered ketones studied by us are analyzed. The determination error is ±0.3%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 942–944, April, 1972.     

Photoisomerization of sterically hindered polymethine dyes

Conclusions In sterically hindered polymethine dyes the photoisomerization process, with the formation of sterically hindered trans and di-cis forms, successfully competes with the nonradiative degradation of the energy on the higher vibrational sublevels of the ground state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1926–1930, August, 1977.     

Claisen rearrangement of sterically hindered N-alkenylindolines

Conclusions Claisen rearrangement of N-(1-methyl-2-butenyl)-2-methyl-2-ethylindoline occurs under mild conditions upon treatment with acids at 20°C. Tricyclic compounds, namely, 6,6-dimethylperhydroeyclopent[g]-2-methyl-2-ethylindoline and 8-methyl-8-ethylpyrrolidino[h, i]-3-methyl-2-ethylindole, were obtained from 7-(1-methyl-2-butenyl)-2-methyl-2-ethylindoline.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 613–618, March, 1987.     

Synthesis and properties of sterically hindered hydroxystyrlpyridines

A number of new sterically hindered hydroxystyrylpyridines were synthesized, and their antioxidative activity as a function of structure was studied. The antitumorigenic characteristics of three of the synthesized compounds are given.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1660–1664, December, 1971.The authors thank L. S. Vasil'eva, R. F. D'yachkovskaya, and N. A. Zakharova for their assistance in this research.     

Synthesis of sterically hindered aromatic aldehydes

Formylation of mesitylene, durene, and m-xylene derivatives containing electron-donor and electron-acceptor substituents by dichloromethyl methyl ether was studied in the presence of TiCl₄. A series of functionally substituted sterically hindered benzaldehydes was prepared from the products of these reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1609–1615, July, 1991.     

Synthesis of sterically hindered aromatic dialdehydes

A study was carried out on the formylation of a series of aromatic compounds containing two mesitylene or durene residues [dimesityl (I), dimesitylmethane (II), 1,2-dimesitylethane (III), 1,6-dimesitylhexane (IV), dimesityl sulfide (V), 1,1-dimesitylethylene (VI), 1,1-dimesityl-1-butene (VII), and didurylmethane (VIII)] by the action of dichloromethyl methyl ether (DCM) in the presence of A1C1₃ and TiCl₄. The corresponding dialdehydes are the major products. The formylation products when the reaction is carried out in the presence of A1C1₃ in the case of (I) and (V) contain significant amounts of monoaldehydes, while partial cleavage of the substrates with the formation of products containing only one benzene ring is observed in the case of (II) and (VIII) in addition to formylation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1700–1703, July, 1991.     

Dipole moments of sterically hindered p-hydroxystyrylpyridines

On the basis of measurements of dipole moments and a comparison of the results obtained with those calculated by a vectorial additive scheme, the structure of a series of sterically hindered p-hydroxystyrylpyridines have been determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1528–1531, November, 1973.     

Synthesis of sterically hindered benzoquinone methacrylates

Sterically hindered p- and o-benzoquinone methacrylates, viz., 2,5-di(tert-butyl)-3,6-di-oxocyclohexa-1,4-dienyl methacrylate and 2,5-di(tert-butyl)-3,4-dioxocyclohexa-1,5-dienyl methacrylate, were synthesized by O-acylation of the lithium and tetrabutylammonium salts of 3,6-di(tert-butyl)-2-hydroxy-p-benzoquinone with methacryloyl chloride. The influence of the nature of cation and solvent on regioselectivity of the acylation was studied. The o-benzoquinone derivative obtained can serve as a paramagnetic ligand in metal complexes.     

Some highly sterically hindered organo-silanols and -siloxanes

Reaction of the iodides TsiSiMe₂I and TsiSiPh₂I, (Tsi  (Me₃Si)₃C) with AgClO₄ in t-BuOH provides a route to the silanols TsiSiMe₂OH and (Me₃Si)₂-C(SiPh₂Me)(SiMe₂OH), respectively. TsiSiMe₂OH gives the disiloxane TsiSiMe₂OSiMe₃ when treated with either (a) Me₃SiOClO₃ (prepared in situ from AgClO₄ and Me₃SiCl) in benzene, (b) Me₃SiI (in the presence of a little (Me₃Si)₂-NH), (c) O,N-bis(trimethylsilyl)acetamide, or (d) MeLi followed by Me₃SiCl. It does not react with Me₃SiCl, but with Me₂SiCl₂ gives TsiSiMe₂OSiMe₂Cl, and with CH₃COCl gives TsiSiMe₂OCOCH₃. The disiloxane is stable to methanolic acid or base, but reacts with KOH in H₂O/Me₂SO and with CF₃COOH to give TsiSiMe₂OH. The disiloxane (Me₃Si)₂C(SiPh₂Me)(SiMe₂OSiMe₃) is formed by treatment of (Me₃Si)₂C(SiPh₂Me)(SiMe₂OH) with Me₃SiI/(Me₃Si)₂NH. Treatment of TsiSiPhMeI with AgClO₄ in t-BuOH gives the silanols TsiSiPhMeOH and (Me₃Si)₂C(SiPhMe₂)(SiMe₂OH) (which with Me₃SiI/(Me₃Si)₂NH give the corresponding disiloxanes) along with some of the t-butoxide (Me₃Si)₂C(SiPhMe₂)(SiMe₂OBu^t).     

New functional derivatives of sterically hindered phenols

Conclusions Dimethylaminoethyl (4-hydroxy-3, 5-ditert-butylphenyl) ketone, in contrast to certain other ketones of a series of sterically hindered phenols, reacts with phenylhydrazine, potassium hydroxide, sodium cyanide, and organic magnesium compounds as a normal -aminoketone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 920–922, April, 1968.The authors thank N.M. Emanuel for his interest in this work in the process of its fulfillment.     

Reaction of sterically hindered o-benzoquinones with diazomethane

Conclusions In contrast to certain o-benzoquinones, the sterically hindered o-quinones react with CH₂N₂ both at the oxygen atoms to give cyclic ethers, and at the C=C and C=O bonds of the quinoid ring; the predominant direction of the reaction depends on the ratio of the reactants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2360–2362, October, 1981.