The ring opening of cyclopropylidene to allene: global features of the reaction surface

Summary The global features of the groundstate ring opening of cyclopropylidene to allene are studied by means ofab-initio FORS MCSCF calculations based on a minimal AO basis set. The energy surface is completely mapped out in terms of three reaction coordinates, namely the CCC ring-opening angle and two angles describing the rotations of the CH₂ groups. For each choice of these three variables, the twelve remaining internal coordinates are optimized by energy minimization. In the initial phase of the reaction, as the CCC angle opens, the CH₂ groups rotate in a disrotatory manner, maintainingC _s symmetry. This uphill reaction path leads to a transition region which occurs early, for a CCC angle of about 84°. In this transition region the reaction path branches into two pathways which are each others' mirror images. The system exhibits thus abifurcating transition region. Passed this region, the two pathways are overall conrotatory in character. However, these downhill reaction paths to the products are poorly defined because, from a CCC opening angle of about 90° on,the CH ₂ groups can rotate freely and isoenergetically in a synchronized, cogwheel-like manner and this disrotatory motion can mix unpredictably with the conrotatory downhill motion. There is no preference for any one of the two reaction pathways yielding the two stereoisomers of allene and the reaction is thereforenonstereospecific with respect to the numbered hydrogen atoms. The global surface is documented by means of contour maps representing slices corresponding to constant CCC angles. The bifurcating transition region is mapped in detail.Operated for the U.S. Department of Energy by Iowa State University under Contract No. 7405-ENG-82. This work was supported by the office of Basic Energy Sciences     

Living and enantiomer-selective polymerization of allene initiated by Ni complex containing chiral phosphine

In the polymerization of chiral allene by using chiral phosphine complex, the polymerization rate of L-1 is approximately 1.9 times that of D-1. This catalyst has enantiomer-selectivity for the polymerization of chiral allene derivative monomer.     

Substitution of both chloro and sulfinyl groups of aryl 1-chlorocyclopropyl sulfoxides in one-pot via cyclopropylmagnesium carbenoids: a synthesis of multi-substituted cyclopropanes

The rearrangement of cyclopropylmagnesium carbenoids, which were generated from aryl 1-chlorocyclopropyl sulfoxides with a Grignard reagent, to allenes was found to be suppressed by adding HMPA as an additive. Alkylation of the cyclopropylmagnesium carbenoids with the Grignard reagent gives mainly alkylated cyclopropylmagnesium chloride instead. The cyclopropylmagnesium chloride intermediate can be trapped with several electrophiles to afford multi-substituted cyclopropanes. This procedure provides a new method for a synthesis of multi-substituted cyclopropanes.     

Synthesis of 3-hydroxy-1-methyl-2-(methylthio) pyrrole from methyl isothiocyanate and prop-2-yn-1-ol

A methylated adduct of lithiated 1-(1-ethoxyethoxy)allene and methyl isothiocyanate undergoes intramolecular cyclization in the presence of CuBr to give 3-(1-ethoxyethoxy)-1-methyl-2-(methylthio)pyrrole. The methanolysis of the latter affords 3-hydroxy-1-methyl-2-(methylthio)pyrrole. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1645–1647, September, 2000.     

联二烯丁基硫醚衍生物合成呋喃的反应

本文报道以联二烯丁基硫醚为起始物的呋喃衍生物的合成方法.实验结果表明,β-联二烯丁基硫醚醇在氢化钠的作用下以很高的收率环化生成一个苯硫基离去的呋喃产物,β-联二烯丁基硫醚醛与外加亲核试剂作用后能得到多一个取代的类似呋喃产物,而β-联二烯丁基硫醚酮在P2O5的促进下也能环化生成呋喃衍生物.     

以炔烃衍生物为底物的联烯合成研究进展

联烯是一类含有累积双键的不饱和化合物, 因其具有重要的生理、药理活性及多种反应活性, 在有机合成中得到了广泛的应用; 随着对联烯性质的深入研究, 联烯的合成方法也日益丰富且各具特色, 其中炔烃衍生物已成为联烯合成的重要前体. 综述了以炔烃衍生物为底物, 经SN2取代、SN2-还原、1,4-加成、迁移、过渡金属催化、开环以及光环化等方式合成联烯的研究进展, 探讨了各种反应历程的特点及其影响因素.     

RAFT polymerization of a novel allene‐derived asymmetrical divinyl monomer: A facile strategy to alkene‐functionalized hyperbranched vinyl polymers with high degrees of branching

Hyperbranched vinyl polymers with high degrees of branching (DBs) up to 0.43 functionalized with numerous pendent allene groups have been successfully prepared via reversible addition fragmentation chain transfer polymerization of a state‐of‐art allene‐derived asymmetrical divinyl monomer, allenemethyl methacrylate (AMMA). The gelation did not occur until high monomer conversions (above 90%), as a result of the optimized reactivity difference between the two vinyl groups in AMMA. The branched structure was confirmed by a combination of a triple‐detection size exclusion chromatography (light scattering, refractive index, and viscosity detectors) and detailed ¹H NMR analyses. A two‐step mechanism is proposed for the evolution of branching according to the dependence of molecular weight and DB on monomer conversion. Controlled radical polymerization proceeds until moderate conversions, mainly producing linear polymers. Subsequent initiation and propagation on the polymerizable allene side chains as well as the coupling of macromolecular chains generate numerous branches at moderate‐to‐high monomer conversions, dramatically increasing the molecular weight of the polymer. AMMA was also explored as a new branching agent to construct poly(methyl methacrylate)‐type hyperbranched polymers by its copolymerization with methyl methacrylate. The DB can be effectively tuned by the amount of AMMA, showing a linear increase trend. The pendent allene groups in the side chains of the copolymers were further functionalized by epoxidation and thiol‐ene chemistry in satisfactory yields. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2959–2969     

新型(Z)-2-[(苯氧基)(芳基)]次甲基-2-丁烯酸酯类化合物的合成

以三苯基膦为催化剂,氮气保护下在苯中实现了取代苯酚与α-取代-2,3-丁二烯酸酯的β'-极化加成反应,合成了16个新型(Z)-2-[(苯氧基)(芳基)]次甲基-2-丁烯酸酯类化合物,其结构经1H NMR,13C NMR和MS(ESI)表征。     

The first example for the asymmetric synthesis of allenes by the Doering-LaFlamme allene synthesis with enantiopure cyclopropylmagnesium carbenoids

The reaction of lithium α-sulfinyl carbanion of enantiopure dichloromethyl p-tolyl sulfoxide with α,β-unsaturated carbonyl compounds gave optically active 1-chlorocyclopropyl p-tolyl sulfoxides having a carbonyl group with high asymmetric induction from the sulfur chiral center. Reduction of the carbonyl group followed by treatment with Grignard reagent, the 1-chlorocyclopropyl p-tolyl sulfoxides resulted in the formation of enantiopure allenic alcohols via the Doering-LaFlamme-type rearrangement of enantiopure cyclopropylmagnesium carbenoid intermediates. This is the first example for the asymmetric synthesis of allenes by the Doering-LaFlamme allene synthesis.     

Ab Initio and DFT Study of the Influence of the Allene Group on the Diels–Alder Reaction

Ab initio and DFT methods were used in combination with various basis sets in order to examine the [4 + 2] Diels–Alder cycloaddition reactions of ethene with 1,3-butadiene, 1,2,4-pentatriene, and 1,2,4,5-hexatetraene with a view to elucidating the role of the allene group in this type of pericyclic reaction. Based on the calculations, the insertion of an allene group decreases the activation energy and increases the exothermal character of the reaction. The decrease is even more marked in the presence of two allene groups, particularly with regard to the reaction enthalpy, which exhibits an additive effect.