Green alder

Xie W., Yu L., Chen D., Li J., Ramirez J., Miranda N. F., Wang P. G. Lanthanide-Catalyzed Organic Synthesis in Protic Solvents in Green Chem. 1998 129, Ed.Anasts P. T. and Williamson T. C., Pb. Oxford Un. Press, Oxford Keywords aza-Diels-Alder reactions, rare earth metals... 

Several different companies have greened various steps of the process. In VNB production by-products come from competing Diels-Alder reactions and polymerization, largely of cyclopentadiene. The reaction is usually carried out in a continuous tube reactor, but this results in fouling, due to polymerization, at the front end, where the dicyclopentadiene is cracked to cyclopentadiene at temperatures over 175 °C. Whilst fouling does not have a very significant effect on yield, over time it builds up. 

In heterocyde synthesis these conditions have been particularly used in 1,3-dipolar cydoadditions and Diels-Alder reactions (Chapt. 9). These conditions are, in fact, ideal for green chemistry . 

Bryant JP, Chapin III FS, Reichardt PB, Clausen TP (1987) Response of winter chemical defense in Alaska paper birch and green alder to manipulation of plant carbon/nutrient balance. Oecologia 72 510-514... 

Earle, M. J., McCormac, P. B. Seddon, K. R. Diels-Alder reactions in ionic liquids a safe recyclable green alternative to lithium perchlorate-diethyl ether mixtures. Green Chem., 1999, 1(1), 23-25 Doherty, S. Goodrich, P. Hardacre, C. et al. Marked enantioselectivity enhancements for Diels-Alder reactions in ionic liquids catalysed by platinum diphosphine complexes. Green Chem., 2004, 6(1), 63-67. 

Green alder A/nas Buds, catkins Snowshoe hare Pinosylvin, pinosylvin Bryant etfl/., 1983 ... 

Green alder J versus M internodes Snowshoe hare J has more pinosylvin and pinosylvin methyl ether Clausen etfl/., 1986... 

Particularly valuable and/or vulnerable parts are protected best. Because of their size and seasonal changes, trees provide instructive examples. In green alder, Alnus crispa, defense compounds, such as pinosylvin, pinosylvin methyl ether and papyriferic acid, are concentrated in buds (2.6% of dry weight) and catkins (1.7%), and least abundant in the internodes (0.05%). Snowshoe hares, L. americanus, reject buds and catkins, while they eat second-year internodes (Bryant etu/., 1983 Clausen eta/., 1986). 

Snowshoe hare Lepus Green alder Afews orispa Pinosylvin, pinosylvin ether... 

Bryant, J. P., Wieland, G. D., Reichardt, P. B., Lewis, V. E., and McCarthy, M. C. (1983). Pinosylvin methyl ether deters snowshoe hare feeding on green alder. Science 222, 1023-1025. 

Furo[3,4-J]pyridazines have also been used in Diels-Alder reactions (331a with maleic anhydride, acrylic acid, 1,4-naphthoquinone, dibenzoyl-ethylene, 1,4-benzoquinone, benzo[c]furandione ° 331c with maleic anhydride) 331a has been shown to be more reactive than 331c. 1,3-Diphenylfuro[3,4-b]quinoxaline (335) has been obtained from phthalide 334 (Eq. 17) as a green crystalline, quite stable solid (mp 244-246°C). In DMSO (deep blue solution), 335 reacts instantaneously with such dienophiles... 

Diphenylfuro[3,4-6 ]quinoxaline (207) has been obtained (70TL1409) from the phthalide (206) as a green crystalline, quite stable solid (m.p. 244-246 °C). In DMSO (deep blue solution), (207) reacts instantaneously with such dienophiles as maleic anhydride, maleimide, dimethyl acetylenedicarboxylate and others to give crystalline adducts which, when heated to or above their melting points, decompose giving a blue color presumably due to reversal of the Diels-Alder reactions. 

Allylzinc halides, with polymer-supported imines, 2, 398 [(7t-Allyl)zirconoxyl]carbenes, preparation, 4, 921 a-Activation, metal fluoroalkyls and fluoroaryls, 1, 735 Altemaric acid, via Alder-ene reactions, 10, 595 Alternative solvents, for green organometallic chemistry fluorous media, 12, 844 ionic liquids, 12, 846... 

Abbott, A.P., G. Capper, D.L. Davies, R.K. Rasheed and V. Tambyrajah, Quaternary Ammonium Zinc- or Tin-Containing Ionic Liquids Water Insensitive, Recyclable Catalysts for Diels-Alder Reactions, Green Chemistry, 4,24—26 (2002). 

The simplest way to look at the ene reaction is to picture it as a Diels-Alder reaction in which one of the double bonds in the diene has been replaced by a C-H bond (green). The reaction does not form a new ring, the product has only one new C-C bond (shown in black on the product), and a hydrogen atom is transferred across space. Otherwise, the two reactions are remarkably similar. 

The green methyl group prefers to be equatorial in the transition state and directs the formatio of the two new chiral centres. The transition state (in the frame) is like a tmm-decalin with two fuse six-membered chair rings. Both new substituents go equatorial in the product while the Lewis aci binds to the oxygen and accelerates the reaction, as it would for a Diels-Alder reaction. 

The elusive dibenzannulated dimethyldihydro-pyrene 69 was prepared by the group of Mitchell (Scheme 16) [48]. A Diels-Alder cycloaddition between an aryne and furan was employed to introduce the key benzene rings to the metacyclo-phanediene framework 68. The colorless 68 switches to green 69 on UV irradiation, and 69 reverts thermally or photochemically. More recently, the same group reported the synthesis of the three-way molecular switch 70 [49]. 

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