A new synthesis of substituted spiro butyrolactones via dyotropic rearrangement

Spiro butyrolactones bearing various α-substituents have been synthesized in three steps from acetic acid derivatives; the sequence employs a dyotropic rearrangement as its pivotal step.     

Substituted 1,3,2,4‐benzodithiadiazines and related compounds

Despite some limitations, the 1:1 condensation of n‐RC₆H₄‐N=S=N‐SiMe₃ (n = 2, 3, 4; R = CH₃, OCH₃, F, Cl, CF₃) with SCl₂, followed by intramolecular electrophilic ortho‐cyclization, was found to be a general synthetic approach to the corresponding 5‐R, 6‐R, and 7‐R–substituted 1,3,2,4‐benzodithiadiazines, formally antiaromatic 12π‐electron compounds. For precursors with n = 3, the high regioselectivity of the cyclization resulted in exclusive (R = OCH₃, F) or predominant (R = CH₃, Cl) formation of 6‐R isomers; the ratio of the major 6‐R isomer to the minor 8‐R one was found to be 72:28 (R = CH₃) or 78:22 (R = Cl). The preferred direction of cyclization is consistent with thermodynamics of the corresponding intermediate σ‐complexes as well as factors of kinetic control for an orbital‐controlled El‐Nu reaction. According to the X‐ray diffraction data, the molecules of 5‐CF₃ (15) and 6‐F (12) derivatives are nearly planar, while the molecules of 5‐OCH₃ (7) and 6‐CH₃ (4) derivatives are bent along the S¹ … N⁴ line by ∼11° (7) or 7° (4). An attempt to adopt CsF‐induced intramolecular nucleophilic ortho‐cyclization of Ar_F‐S‐N=S=N‐SiMe₃ into polyfluorinated 1,3,2,4‐benzodithiadiazines for polyfluoropyridine derivatives resulted in formation of polyfluorinated aminopyridines. Data obtained are consistent with a previously suggested scheme of sulfur–nitrogen chain shortening during cyclization. Mild acid hydrolysis of the title compounds was shown to be a convenient synthetic route to substituted 2,2′‐diaminodiphenyl disulfides (including polyfluorinated ones) via the corresponding 2‐aminobenzenethiols. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 113–124, 1999     

Thermal decomposition of cyclopentane and related compounds

Cyclopentane has been decomposed in comparative-rate single-pulse shock-tube experiments. The pyrolytic mechanism involves isomerization to 1-pentene and also a minor pathway leading to cyclopropane and ethylene. This is followed by the decomposition of 1-pentene and cyclopropane. The rate expressions over the temperature range of 1000°–1200° K are Details of the cyclopentane decomposition processes are considered, and it appears that if the trimethylene radical is an intermediate, then ΔH_f(trimethylene) ≤ 280 kJ/mol at 300°K.     

Formation of novel polycyclic cage compounds through ‘uncaging’ of readily accessible higher cage compounds

The synthesis of the novel cage compounds 7-halomethyl-8-(carbomethoxy)tetracyclo[4.2.1.1^4,7.0^2,5]deca-3-(11)-ene-10-ones, methyl-4-methylene-6-oxopentacyclo[5.4.0.0.^2,5.0^3,10.0^7,9]undecane-9-carboxylate, 3-chloromethyl-4-(carbomethoxy)tetracyclo[4.2.1.1.^3,8.0^2,5]deca-7(11)ene-10-one, 2-bromo-5-methyl-8-methylene-6-oxotricyclo[5.3.0.0^3,9]decane-4-carboxylic acid and 2-bromo-5-methyl-8-methylene-6-oxotricyclo[5.3.0.0^3,9]decane-4-methyl carboxylate, achieved through base catalyzed rearrangement, is described.     

Electron-impact studies—LXXIV: A survey of rearrangement processes in the ‘doubly-charged ion’ mass spectra of aromatic compounds

The technique of Beynon² has been used to determine the ‘doubly-charged ion’ mass spectra of a variety of aromatic compounds which contain pronounced rearrangement peaks in their conventional mass spectra. Many, but not all, of the ‘doubly-charged ion’ spectra contain similar rearrangement peaks to those observed in conventional spectra.     

Recent advances in the semi-pinacol rearrangement of alpha-hydroxy epoxides and related compounds

The semi-pinacol rearrangement is fast becoming an extremely reliable reaction in organic synthesis allowing the rapid construction of relatively complex stereodefined products in high yield. Recent advances in asymmetric synthesis have also enabled enantiopure precursors to partake in the rearrangement showing that extremely high levels of stereospecificity are observed. In this critical review recent advances in the semi-pinacol rearrangement over the past 15 years are examined which demonstrate the extremely high utility of this reaction towards the development of structurally diverse organic building blocks (74 references).     

Bonding and reactivity in π-allyl—metal compounds

The π-allyl group of π-C₃H₅Co(CO)₃ has two angles of tilt, one of which (from semi-empirical molecular orbital calculations) is stabilised principally by the influence of the C(p_v) orbitals of the terminal carbon atoms, which form part of the σ-framework of the π-allyl group, and the other of which is stabilised by a balance between bonding orbital components of the central and terminal carbon atoms. The Co(CO)₃ moiety has asymmetric bonding, with one CO group more weakly bonded to the metal atom. The asymmetric bonding of the Co(CO)₃ moiety is primarily caused by the electronic character of the π-allyl group, but is significantly influenced by the magnitude of the τ-tilt angle of the π-allyl group. The relatively high reactivity of π-C₃H₅Co(CO)₃, compared with the reactivity of π-C₃H₅Fe(CO)₂NO, Co(NO)(CO)₃, or Ni(CO)₄, is explained by the relatively weak bonding of a CO group to the metal atom and a possible explanation of the anomalous relative rates of the reactions of π-C₃H₄RCo(CO)₃ (R = H, 1-CH₃, 2-CH₃, 1-Cl, 2-Cl) with P(C₆H₅)₃ is indicated.The angles of tilt of the π-allyl group and the asymmetric bonding of the π-cyclopentadienyl moiety in [π-C₃H₄Ni(π-C₅H₅)]₂ are caused by factors similar to those in π-C₃H₅Co(CO)₃.     

Low–energy,low-temperature mass spectra. 8—The McLafferty rearrangement

The McLafferty rearrangement giving rise to the McLafferty ion, the complementary ion and a protonated molecule is discussed in the cases of the alkenes, alkanals, alkanones, alkanoic acids and alkanoic esters, in terms of the low-energy, low-temperature mass spectra. Based on the behaviour of the alkanals, which show a series of peaks corresponding to [M ? C_nH_2n]⁺˙, it is suggested that these also involve McLafferty rearrangements from rearranged distonic ions. The same processes are held to be responsible for similar series of peaks in the case of the alkenes and that of the amines. Where possible the energetics of the processes concerned are discussed. The low-energy mass spectra of the linear alkenes propene to octene and those of the octenes are reported.     

The neutral and ionic vinylidene—acetylene rearrangement

Transition state structures for the neutral, cationic and anionic vinylidene—acetylene rearrangement are calculated by ab initio methods. While the barriers for the neutral and cationic H-shift are found to be low or even zero involving a planar structure, rearrangement of the vinylidene anion proceeds with high activation energy possibly via a perpendicular transition state.     

Fluorovinyl organometallic compounds — an historical review and some recent advances

This review describes the historically important routes to fluorovinyl organometallic species of the type M-(CX=CX₂), where M is a main-group or transition-metal element and one, or more, of the substituent atoms, X, is fluorine, the others being either other halogens, or hydrogen. A number of newer synthetic methods are described which have resulted in the preparation of a wider range of examples of such compounds. The structure, spectrocopy, properties, reactivity and future prospects for this class of compounds are described.     

Metallacyclopentadienes and related heterocycles via 1,1‐organoboration of alkyn‐1‐ylmetal compounds

Metallacyclopentadienes (metalloles) containing M = Si, Ge, Sn, Pb, Ti, Pt can be prepared by 1,1‐organoboration of alkyn‐1‐ylmetal compounds L_nM CC R¹(R¹ = H, alkyl, aryl, silyl, etc; L depends on M, and can be hydrogen, alkyl, aryl, Cl, Br, amino groups, a chelating diphosphane, and one or more L can be again alkynyl groups). These reactions proceed via activation of the M C bond(s) by an electron‐deficient triorganoborane BR₃ (R = alkyl, aryl; non‐cyclic, monocyclic, bicyclic, and tricyclic boranes), at first intermolecular and then intramolecular. In the course of these reactions, the M C bonds are cleaved, zwitterionic alkynylborate‐like intermediates are formed, in which the metal‐containing fragments are coordinated side‐on to the CC bonds. In most cases, the 1,1‐organoboration reactions tolerate various functional groups at the alkyne as well as at the metal. The characterization of intermediates and final products by X‐ray structural analysis and by multinuclear magnetic resonance spectroscopy (NMR) is documented and described. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:188–208, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20222     

Pyrolysis reaction of carpronium chloride and its structurally related compounds. 2—a mass spectrometric study of the lactonization mechanism

The mechanism of the pyrolysis reaction of carpronium chloride [(CH₃)₃N⁺? (CH₂)₃? COOCH₃CI^?] leading to γ-butyrolactone and tetramethylammonium chloride was investigated by means of thermal analysis, pyrolysis gas chromatography mass spectrometry and field desorption mass spectrometry, using deuterium labelling. The results indicated that carpronium chloride pyrolysed to yield equimolar amounts of γ-butyrolactone and tetramethylammonium chloride, methyl transfer occurred between N and O during the pyrolysis process. The mechanism is discussed on the basis of the experimental results, and with the aid of the theoretical results calculated by the CNDO/2 method. The mechanism presented is as follows. γ-Butyrolactone is formed by the intramolecular migration of the π-orbital of C?O to the carbon adjacent to [(CH₃)₃N]⁺ via a 5-membered ring transition state, accompanied by a bimolecular reaction between [(CH₃)₃N]⁺ and the CH₃ of O? CH₃, resulting in the formation of tetramethylammonium chloride in an amount equimolar with γ-butyrolactone.