Dienone-phenol transformations in the reaction of 4, 6-di-tert-butylspiro [2.5]-3, 6-octadien-5-one with organomagnesium compounds

Conclusions 4, 6-Di-tert-butylspiro[2.5]-3,6-octadien-5-one when reacted with Grignard reagents opens the three-membered ring, with the formation of either the 4-alkyl-2,6-di-tert-butylphenol or the 4-(-haloethyl)-2,6 -di-tert-butylphenol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1155–1157, May, 1967.     

Ab initio study of mechanism of forming a Spiro-Si-heterocyclic ring compound

The mechanism of the cycloaddition reaction of forming a spiro-Si-heterocyclic ring compound between singlet dichloroalkylidenesilylene (Cl₂C=Si:) and ethene has been investigated with CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has one dominant reaction pathway. The presented rule of this reaction is that the 3p unoccupied orbital of Si in dichloroalkylidene and the π orbital of ethene forming the π → p donor-acceptor bond, resulting in the formation of a three-membered ring intermediate. Ring-enlargement effect make the three-membered ring intermediate isomerizes to a four-membered ring silylene. Due to sp ³ hybridization of Si atom in the four-membered ring silylene, the four-membered ring silylene further combines with ethene to form a spiro-Si-heterocyclic ring compound.     

Influence of the heteroatom on the structure,bonding and ring strain of a series of three-membered rings containing a second,third, fourth and fifth row elements: a theoretical investigation

Three-membered heterorings have received a great interest for the design of organic reactions and new active therapeutic agents. However, there is little information available in the literature about their structural properties, in particular for those containing third, fourth, and fifth row elements. With this in mind, structure, bonding, ring strain, and Mulliken charge distribution of a series of 22 saturated three-membered rings containing a second, third, fourth, and fifth row element were theoretically investigated. Calculations were carried out within the MP2, PBE1PBE, and CCSD approximations using Pople’s and correlation consistent basis sets. In general, structural predictions obtained by MP2 and coupled cluster are comparable with each other for the studied heterocycles, and their predictions are in good agreement with the little experimental data available. The structural parameters, ring strain, and Mulliken charges are strongly affected by the nature of heteroatom contained into ring skeleton, finding a consistent periodic relationship according to the row-group or row-period plot. The ring geometry was highly symmetric in most of the studied cases (C_2h), except for the rings containing V-group elements (C_s) whose molecular symmetry is distorted by the disposition out of molecular plane of H-heteroelement bond. Finally, the increase of heteroatomic radius increases significantly the molecular strain of these three-membered heterocycles, being especially notable in the four and fifth row element rings. Curiously, the rings containing tellurium, iodium, bromo, chloro, and sulfur presented a ring strain comparable to those common heterocycles containing second row element.     

The hydrolytic stability of the three-membered ring of alkyl- and alkoxy-β-(ethyleneamino)ethylsilanes

Conclusions The hydrolytic stability of the ethyleneimine ring in trialkyl- and trialkoxy--(ethyleneamino) ethylsilanes in aqueous media has been studied and the possibility of obtaining organosiloxanes containing the three-membered ethyleneamine ring in the-position to the silicon atom has been shown.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1129–1132, May, 1969.     

Some new aspects of bonding in cyclopropane

The peculiar properties of the three-membered ring in cyclopropane are partially due to characteristic relaxation effects of the carbon orbitals in the molecule. AO contraction in the two strongly C? C bonding MO's of A type is essential for the stability of the C₃ ring, whereas AO expansion in the E'-type HOMO contributes to the π character of the peripheral C? C bonds.     

Opening of the three-membered ring in 4,6-di-tert-butylspiro[2,5]octa-3,6-dien-5-one under the action of magnesium halides

Conclusions The three-membered ring in 4,6-di-tert-butylspiro[2,5]octa-3,6-dien-5-one opens under the action of magnesium halides with the formation of 4-(-haloethyl)-2,6-di-tert-butylphenols.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 930–932, April, 1967.     

Hydroxymercuration-demercuration of 3-carene

Conclusions It was found that Hg(OAc)₂ adds to 3-carene both to the double bond and to the three-membered ring; the formation of-4-caranol and trans-1,8-terpin as demercuration products is in agreement with the trans-addition of the mercury salt to the double bond.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 385–388, February, 1972.     

13C NMR spectra of 20-ketosteroids with 16α,17α three-membered ring

Conclusions ¹³C chemical shifts have been determined for 20-ketosteroids with a 16, 17 three-membered ring (X=S, NH, NAc, O, CH₂), and a linear relationship has been found between the -effects of X and the calculated changes in electron density on the C atoms C¹⁶ and C¹⁷; the - and -effects depend on the electronegativity of X. The C¹⁶ and C¹⁷ centers in the epoxysteroid (X=0) are more electrophilic than in the other analogs that were studied; this is consistent with the observed higher reactivity of the epoxide ring in reactions of cleavage by nucleophilic reagents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2189–2194, October, 1987.     

Synthesis of five-membered heterocyclic compounds from perfluoro-α-lactam

Conclusions 1-(Perfluoro-tert-butyl)-3,3-bis(trifluoromethyl)aziridin-2-one enters into cyclic addition reactions with carbonyl compounds and with nitriles, forming oxazolidones and imidazolones. Cyclic addition to perfluoro--lactam takes place, depending on the type of reagent, with rupture of any of the bonds in the three-membered ring.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2343–2346. October, 1981.     

Pentacoordinate 1H-phosphirenes: reactivity, bonding properties, and substituent effects on their structures and thermal stability

The synthesis, reactivity, and bonding properties of several pentacoordinate P-phenyl-substituted 1H-phosphirenes are discussed. X-ray crystallographic analysis of one of them reveals a highly distorted square pyramidal (SP) arrangement around the phosphorus. NMR studies confirm that they retain the SP structure in solution and demonstrate that the endocyclic P-C bonds in the three-membered ring have a very high degree of p character, which results from their being both basal bonds in the SP structure and endocyclic bonds of the three-membered ring. Structural parameters of the three-membered ring of the pentacoordinate phosphirenes obtained by experiment and theoretical calculations are very close to those of a tetracoordinate phosphirenium cation. Thus, by analogy with tetracoordinate phosphirenium cations, it can be considered that a sigma-pi interaction between the sigma orbital of the apical bond and the pi orbital of the C=C bond in the three-membered ring is operative in pentacoordinate phosphirenes. The sigma-pi interaction is found to lower the reactivity of the C=C bond of the three-membered ring. The reactivities of the pentacoordinate phosphirenes are also affected by the substituent on the carbon atom in the three-membered ring.     

Synthesis and study of spiro [(indane-1,3-dione)-2,3′-azir-1′-ines] and their cleavage products

Spiro[(indane-1,3-dione)-2,3 (2-substituted 1-azirines)] were obtained by intramolecular cyclization of 2-acylindane-1,3-dione oximes. Their structures and properties were investigated, and it was established that the C-N and C-C single bonds are cleaved during opening of the three-membered ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 65–69, January, 1976.     

Transformed steroids

Conclusions The opening of the three-membered ring of 16, 17-methylenepregn-5-en-3-ol-20-one by nucleophilic reagents in the presence of H₂SO₄, proceeds regiospecifically, depending on the nature of the nucleophilic reagent.See [1] for Communication 118.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 658–662, March, 1980.     

Structure, strain, and degenerate rearrangement of tricyclo[2.1.0.0 1,3]pentasilane and related molecules

We theoretically investigate a highly strained tricyclic silane (tricyclo[2.1.0.0 1,3]pentasilane (4b), an isomer of pentasila[1.1.1]propellane (3b)) composed of three fused three-membered rings. The central ring is distorted. One of the fusion bonds in the central ring is shorter than the normal Si-Si single bond (2.350 A) whereas the other is as long as the fusion bonds in bicyclo[1.1.0]tetrasilane (2b) (2.860 A) and 3b (2.778 A). The tricyclic silane is less strained than the carbon congener and more strained than the isomer 3b. The electron delocalization between one of the fusion bonds and the geminal Si-Si ring bonds elongates the fusion bond and stabilizes the molecules to reduce the strain. The silanes composed of the fused three-membered rings are less strained than the carbon congener. A degenerate rearrangement of a three-membered ring is predicted. The enthalpy of activation of the rearrangement of the distorted central ring is low (7.2 kcal/mol) for 4b, but appreciable (22.3 kcal/mol) for the germanium congener, tricyclo[2.1.0.0(1,3)]pentagermane (4c). We investigate the effects of the substituents on the distortion of the central three-membered ring and the degenerate rearrangement.     

Vilmoraconitine, a novel skeleton C19-diterpenoid alkaloid from Aconitum vilmorinianum

A novel C₁₉-diterpenoid alkaloid vilmoraconitine (1) was isolated from the roots of Aconitun vilmorinianum. Its structure was mainly determined by MS, 2D NMR, and X-ray methods. This is the first aconitine-type C₁₉-diterpenoid alkaloid with one three-membered ring at C-8, C-9, and C-10.     

13C NMR spectra of gem-dichlorocyclopropyl aryl selenides

Conclusions The¹³C NMR spectra of a number of cyclopropyl aryl selenides were discussed for the first time and it was shown that p- interaction is absent between the three-membered ring and the ArE fragment, where E=0, S, Se.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2410–2412, October, 1978.     

Ring-opening and ring-expansion reactions of carborane-fused borirane

Though the reaction chemistry of three-membered ring molecules such as cyclopropanes and their heteroatom-containing analogues has been extensively studied, the chemical properties of their boron analogues, boriranes, are little known thus far. This work describes the diverse reactivity patterns of carborane-fused borirane 2. This borirane engages in ring-opening reactions with different types of Lewis acids, such as BBr₃, GeCl₂, GaCl₃, BH₃(SMe₂) and HBpin, affording a series of ring-opening products, in which M–X or B–H bonds add across the B–C(cage) bond of the three-membered ring in 2. On the other hand, borirane 2 can undergo ring-expansion reactions with unsaturated molecules such as PhCHO, CO₂ and PhCN to give ring-expansion products, five-membered boracycles, via a concerted reaction mechanism as supported by DFT calculations. The results of this work not only enrich the reaction chemistry of boriranes, but also offer new routes to boron-containing compounds and heterocycles.

Carborane-fused borirane can not only engage in ring-opening reactions with different types of Lewis acids, but also undergo ring-expansion reactions with unsaturated molecules such as PhCHO, CO₂ and PhCN to give five-membered boracycles.     

New type of transannular reactions in azirine-fused medium-size heterocycles: Selective transformations of azirino[2,1-<Emphasis Type="Italic">e</Emphasis>][1,6]benzoxazocines and -benzothiazocines into oxa(thia)zine and oxa(thia)zole derivatives

Opening of the three-membered ring in heterocyclic systems incorporating a dichloroaziridine ring fused to eight-membered O,N-or S,N-heterocycles is accompanied by transannular reactions with participation of the endocyclic oxygen and sulfur atoms. Depending on the conditions, the products are 1,4-benzoxazine (1,4-benzothiazine) or 1,3-benzoxazole (1,3-benzothiazole) derivatives. The discovered transformations were used as a basis of methods for the preparation of new heterocyclic systems, 2,3,4,4a-tetrahydro-1H-pyrido-[3,2-b][1,4]benzoxa(thia)zine derivatives, in domino or consecutive modes, as well as of pyrrolidinyl-substituted 1,3-benzoxa(thia)zoles.     

Conglomerate crystallization in organic compounds II. The conformation,configuration, and spontaneous resolution of 1-phenyl-2-cyano-cyclopropane

The crystal structure of 1 -phenyi-2-cyano-cyclopropane was investigated to probe the stereochemical effects of placing different groups at the 2-position of the phenylcyclopropane moiety. The substance crystallized in space group P2₁2₁2₁ with cell constants a=16.921(3), b=7.699(2), and c=6.251(2) Å; V=814.33 ų and D (calc; z=4) =1.168 g·cm^–3. Final R(F)=0.04, using unit weights. The phenyl substituent is almost exactly in the bi-secting conformation with respect to the C-C-C angle at the point of attachment to cyclopropane. The average value of the C-C distances in the three-membered ring is 1.501 Å, which is on the low side of the ranges cited in previous studies. When we apply the additivity principle to our measured geometrical data and calculate the asymmetry parameters, the value of _cns [0.012(3)] is a little low, but within experimental error it is in accord with the value (0.017) given by Allen. However, our value of _cns (0.006(3)] is substantially lower than Allen's, which is surprising, since the bisecting phenyl ring can exert its maximum effect on the asymmetry of cyclopropane. The substance undergoes spontaneous resolution into a conglomerate of chiral crystals. Unfortunately, in the absence of anomalous scatterers, the absolute configuration could not be determined; nonetheless, the space group in which the compound crystallizes is P2₁2₁2₁, which leaves no ambiguity to the fact that the crystals are a conglomerate.     

X-ray structural studies of several novel nitrocyclopropanes

The x-ray crystal structures forcis,cis- andtrans,trans- 2,3-dimethyl-1-nitrocyclopropanecarboxylic acid, 2,2,3,3-tetramethyl-1-nitrocyclopro-panecarbonitrile, 2,2,3,3-tetramethyl-1-nitrocyclo-propanecarboxamide, andtrans,trans,trans,trans-2,2,3,3-tetramethyl-1,1-dinitrobicyclopropyl are reported. Contrary to expectations, -accepting groups that are syn to dimethyl substituents prefer a conformation perpendicular to the three-membered ring when there is an sp² electron-withdrawing substituent also bonded to the same carbon atom. Ab initio calculations are reported for model compounds and these results are compared with the experimentally determined ones.