Controlling Factors Determining The Selective Hscn Addition To Double Bonds And Their Application To The Synthesis Of 7-isothiocyano-7,8-α-dihydro-bisabolene

The reactivity of terminal and trisubstituted double bonds of monoterpenes with HSCN has been examined by GC giving evidence that kinetics is responsible for the chemoselective addition to terminal double bonds in terpenes. The results show that the addition to the terminal double bond is about 17 times faster than for trisubstituted double bonds and that the presence of the first SCN group in the molecule prevents a second addition. The presence of a hydroxyl or methoxy group in the molecule, decreases the reaction kinetics. Based on these kinetic experiments a two steps synthesis of the natural product 7-isothiocyano-7,8-dihydro-α-bisabolene using bisabolol as starting material, was planned and successfully accomplished.125661666Drobnica, L., Kristían, P., Augustín, J., The Chemistry of the Cyanates and Their Thio Derivatives, , Saul Patai Ed., John Wiley & Sons, New YorkEdenborough, M.S., Herbert, R.B., (1988) Nat. Prod., p. 229Faulkner, D.J., (1994) Nat. Prod., p. 355(1993) Nat. Prod., p. 497(1992) Nat. Prod., p. 323(1991) Nat. Prod., p. 97(1990) Nat. Prod., p. 269(1988) Nat. Prod., p. 613Fraga, B.M., (1994) Nat. Prod. Rep., p. 533Piers, E., Young, B.W.A., Rettig, S.J., (1987) Tetrahedron, 43 (23), p. 5521Piers, E., Yeung, B.W., (1986) Can. J. Chem., 64, p. 2475Chenera, B., Chuang, C.P., Hart, D.J., Lai, C.S., (1992) J. Org. Chem., 57, p. 2018Da Silva, C.C., Almagro, V., Zukerman-Schpector, J., Castellano, E.E., Marsaioli, A.J., (1994) J. Org. Chem., 59, p. 2880Da Silva, C.C., Almagro, V., Marsaioli, A.J., (1993) Tetrahedron Lett., 34, p. 6717Martin, V.S., Woodward, S.S., Katsuki, T., Yamada, Y., Ikeda, M., Sharpless, K.B., (1981) J. Am. Chem. Soc., 103, p. 6237Rakels, J.L., Straathof, A.J.J., Heijnin, J.J., (1993) Enzyme Microb. Technol, 15, p. 1051Diveley, W.R., Buntin, G.A., (1969) J. Org. Chem., 34, p. 616Queiroga, C.L., Ferracini, V.L., Marsaioli, A.J., (1996) Phytochemistry, 42, p. 1097(-)Bisabolol (8) [(αS, 1S)-1-methanol-α,4-dimethyl-α-4-methyl-3-pentenyl-3-cyclohexene] was obtained from commercial candeia oil (CITRÓLEO - S.Paulo, SP, Brazil)Sullivan, B.W., Faulkner, D.J., Okamoto, K.T., Chen, M.H.M., Clardy, J., (1986) J. Org. Chem., 51, p. 5134Dubois, J.E., Lomas, J.S., (1971) Tetrahedron Lett., 7, p. 599Delay, F., Ohloff, F., (1979) Helv. Chem. Acta, 62, p. 326A sample of dihydrolimonene was kindly provided by Prof. Marcio C. S. de Mattos from IQ/UFRJ, RJ, Brazi

Freezing in random graph ferromagnets

Using T=0 Monte Carlo and simulated annealing simulation, we study the energy relaxation of ferromagnetic Ising and Potts models on random graphs. In addition to the expected exponential decay to a zero energy ground state, a range of connectivities for which there is power law relaxation and freezing to a metastable state is found. For some connectivities this freezing persists even using simulated annealing to find the ground state. The freezing is caused by dynamic frustration in the graphs, and is a feature of the local search-nature of the Monte Carlo dynamics used. The implications of the freezing on agent-based complex systems models are briefly considered.Comment: Published version: 1 reference deleted, 1 word added. 4 pages, 5 figure

Quantum Erasure by Transverse Indistinguishability

We show that the first experiment with double-slits and twin photons detected in coincidence can be understood as a quantum eraser. The ``which path'' information is erased by transverse indistinguishability obtained by means of mode filtering in the twin conjugated beam. A delayed choice quantum eraser based on the same scheme is proposed.Comment: Submitted for publication in Optics Communication

Revisiting consistency conditions for quantum states of systems on closed timelike curves: an epistemic perspective

There has been considerable recent interest in the consequences of closed timelike curves (CTCs) for the dynamics of quantum mechanical systems. A vast majority of research into this area makes use of the dynamical equations developed by Deutsch, which were developed from a consistency condition that assumes that mixed quantum states uniquely describe the physical state of a system. We criticise this choice of consistency condition from an epistemic perspective, i.e., a perspective in which the quantum state represents a state of knowledge about a system. We demonstrate that directly applying Deutsch's condition when mixed states are treated as representing an observer's knowledge of a system can conceal time travel paradoxes from the observer, rather than resolving them. To shed further light on the appropriate dynamics for quantum systems traversing CTCs, we make use of a toy epistemic theory with a strictly classical ontology due to Spekkens and show that, in contrast to the results of Deutsch, many of the traditional paradoxical effects of time travel are present.Comment: 10 pages, 6 figures, comments welcome; v2 added references and clarified some points; v3 published versio