Ab initio study of the Wolff rearrangement of C6H4O intermediate in the gas phase

Ab initio calculations of the geometry and reactivity of 1,2-ketocarbene C₆H₄O as an intermediate in organic reactions were performed using the second-order Møller-Plesset (MP2) perturbation theory in the 6-311G^* basis set. Only the singlet state of the intermediate was considered. An oxirene-like structure (6) with a six-membered ring and a ketene-like structure (5) with a five-membered ring were localized on the potential energy surface. Attempts to locate a quinone type structure characteristic of aliphatic ketocarbenes failed. The energy of structure5 is ?70 kcal mol^?1 lower than that of structure6. Harmonic frequencies and intensities of normal vibrations in the IR spectra of6 and5 were calculated. The activation energy of the Wolff rearrangement6→5 was estimated at 12.5 kcal mol^?1. The geometry of the transition state of this reaction resembles the quinone-like structure.     

The molecular mechanism of novolak-diazonaphthoquinone resists

Novolak-diazonaphthoquinone (DNQ) resists are photosensitive varnishes that are used in the fabrication of more than 80% of today's integrated circuits. They have played a crucial role in an unprecedented technical revolution, yet until quite recently nobody really knew how they work. We have been concerned with this problem for some time and we realize now that the principal functions of novolak resists, namely the inhibition by DNQ derivatives of the dissolution of novolak films, and the cessation of inhibition on exposure to radiation, are essentially physical phenomena. Dissolution inhibition is caused by an electric stress imposed on the phenol groups of the resin by the inhibitor. This effect penetrates deep into the material through the formation of hydrogen-bonded phenolic strings. Exposure relieves the stress by uncoupling the strings from the source of induction. The concept of phenolic strings is new and unusual, but it is essential for the understanding of dissolution inhibition. With it, all the many aspects of novolak resists can be interpreted in a unified manner.     

Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic ammonium ylides

An investigation of the Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic ammonium ylides has been conducted by employing various bases and boron Lewis acids. Using BBr₃ together with the phosphazene base 6, various allylic amines could be rearranged in good yields with low to excellent diastereoselectivity.     

Facile [3,3]-sigmatropic rearrangement in the reaction of α-chloroperfluorostyrene with allyl alcohol

The reaction of -chloroperfluorostyrene (1) with allyl alcohol in the presence of KOH at 45–50°C leads to a mixture of the allyl 2-pentafluorophenyl-2-chloro-4-pentenoate (2) and the product of the addition of the starting reagents (3). Ester2 is formed as the result of a mild [3,3]-sigmatropic rearrangement of the reaction intermediate.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1925–1926, August, 1992.     

Synthesis of functionalized polycyclic compounds via a novel aromatic oxy-Cope rearrangement

Polycyclic compounds have been prepared by aromatic dianionic oxy-Cope rearrangements involving the π bonds of two phenyl rings in a [3,3] sigmatropic rearrangement.     

2-(Methylthio)pentafluoropropene

2-(Methylthio)pentafluoropropene was obtained by dehydrofluorination of methyl 2H-hexafluoroisopropyl sulfide by the BF₃ · NEt₃ complex. Its reactivity with respect to allyl alcohol and hexamethyldisilazane was studied. The electrophilicity of 2-(methylthio)penta-fluoropropene was compared with the properties of terminal polyfluoroalkenes whose behavior in these reactions has been studied previously.Perfluoroisobutylene also reacts with allyl alcohol in the absence of protophilic agents.3,4Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 80–84, January, 1994.     

环己酮肟在改性氧化锆催化剂上的Beckmann重排反应Ⅴ.活化焙烧温度对B2O3/ZrO2催化剂的影响

 采用BET，XRD，TG－DTA，FT－IR，XPS和NH3－TPD等分析手段，研究了活化焙烧温度（500～800℃）对B2O3／ZrO2催化剂织构／结构、表面性质和环己酮肟气相重排反应的影响．催化剂活化焙烧温度升高促进了ZrO2向单斜晶相转化，同时活性组分氧化硼由以BO4为主要结构单元的物种转变为以BO3为基本结构单元的B2O3，导致催化剂比表面积、孔体积以及表面酸量减小，ZrO2与B2O3之间的相互作用减弱．700℃活化焙烧的催化剂表面拥有最大比例的中强酸中心，而且Beckmann反应的活性稳定性最高．这些结果表明，活化焙烧温度对B2O3／ZrO2催化剂上气相重排反应的影响主要是通过改变催化剂中B原子的配位状态和表面酸性实现的．     

Synthesis of 4-dialkylaminopyridine derivatives through ring-rearrangement of 3-nitro-2H-pyran-2-one acetamidines

A new synthesis of substituted 4-dialkylaminopyridines was developed, starting from 3-nitropyran-2-one N-functionalized amidines. Secondary amines were reacted with the amidines in a sealed tube and in ethanol as the solvent yielding exclusively 4-dialkylaminopyridine derivatives or a mixture with 4-methylpyridine derivative, depending on the C-α-linked substituents of the starting amidine. Structural elucidation of the 4-dialkylaminopyridines revealed their existence as two tautomeric forms, depending on the solvent.     

Experimental and theoretical approaches into the C- and D-ring problems of sterol biosynthesis. Hydride shift versus C-C bond migration due to cation conformational changes controlled by the counteranion

The C- and D-ring problems of sterol biosynthesis, how an enzyme overcomes the Markovnikov wall, were investigated by using a model compound from an experimental as well as theoretical standpoint. When model diol 20 was treated with BF₃·Et₂O, SnCl₄, TiF₄, Sc(OTf)₃, FeCl₃, or TfOH, spirocyclic ether 21 was formed as the sole product via a tert-cationic intermediate 16 through 1,2-hydride shift. However, the treatment with TiCl₄ afforded six-membered ring products 22, 23, 24, 25, 26, and 27 via the ring expansion into the unstable six-membered ring secondary cation 17. Occurrence of both α and β chloride 23 and 24 is distinctive evidence of the existence of secondary cation 17, ruling out the idea of the concerted mechanism. Molecular mechanics calculations of the naked cation 15 elucidated two possible conformers, parallel 15-I (five membered ring and cationic plane) that is favorable for the hydride shift generating 16 and perpendicular 15-II leading to C-C bond migration to 17. The first ab initio calculation of the cation conformation in the presence of counteranions such as [TiCl₄OH]⁻, [TiF₄OH]⁻, [BF₃OH]⁻, and [OTf]⁻ entirely supported our experimental results. Although the counteranion [TiCl₄OH]⁻ stabilizes perpendicular cation 15-II, it destabilizes the parallel conformer 15-I significantly, and thus, the C-C bond migration to 17 becomes the only possible pass. On the other hand, [TiF₄OH]⁻, [BF₃OH]⁻, and [OTf]⁻ stabilize parallel conformer 15-I and the hydride shift to 16 becomes the only possible pass. The relative location or distance of the counteranion from the cation should be the biggest factor to control the stability and, thus, the conformation of the cation. Our results indicate that the carboxylate anions in the enzyme cavity enable to control the conformation of pre-C-ring cationic intermediate 3 to be perpendicular leading to six-membered C-ring secondary cation 4. The parallel conformation of the cation 5 could lead to hydride shift to give tirucallanoids or lanostanoids. Therefore, this result is the first example that overcame the big Markovnikov wall experimentally and theoretically at least to our knowledge.