- Palladium-catalyzed asymmetric synthesis of allylic fluorides
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The enantioselective fluorination of readily available cyclic allylic chlorides with AgF has been accomplished using a Pd(0) catalyst and Trost bisphosphine ligand. The reactions proceed with unprecedented ease of operation for Pd-mediated nucleophilic fluorination, allowing access to highly enantioenriched cyclic allylic fluorides that bear diverse functional groups. Evidence that supports a mechanism in which C-F bond formation occurs by an SN2-type attack of fluoride on a Pd(II)-allyl intermediate is presented.
- Katcher, Matthew H.,Doyle, Abigail G.
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supporting information; experimental part
p. 17402 - 17404
(2011/02/23)
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- On the isolation of neat allylic fluorides
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Neat cinnamyl fluoride, geranyl fluoride, 5-carbomethoxy-3-fluorocyclohexene and parent 3-fluorocyclohexene undergo spontaneous decomposition on contact with borosilicate glass or catalytic quantities of moderately strong acids that consists in polycondensation with elimination of HF initiated by electrophilic abstraction of F-. Acid sensitivity of these allylic fluorides correlates with stability of respective allylic cations, exceeds that of parent benzyl fluoride, yet can be mitigated by the use of Teflon and PFA containers that permit their isolation and handling in the neat state.
- Lee, Eunsung,Yandulov, Dmitry V.
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scheme or table
p. 474 - 483
(2009/12/06)
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- A mild and efficient method for the stereoselective formation of C-O bonds: Palladium-catalyzed allylic etherification using zinc(II) alkoxides
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(equation presented) A highly chemo-and stereoselective palladium-catalyzed allylic etherification reaction is described. The use of zinc(II) alkoxides proved effective in promoting the addition of the oxygen nucleophile derived from aliphatic alcohols to η3-allylpalladium complexes. Using diethylzinc (0.5 equiv), 5 mol % of Pd(OAc)2, and 7.5 mol % of 2-di(tert-butyl)phosphinobiphenyl in THF, the cross-coupling reaction between various aliphatic alcohols and allylic acetates proceeded at ambient temperature to furnish allylic ethers with high stereoselectivity.
- Kim, Hahn,Lee, Chulbom
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p. 4369 - 4371
(2007/10/03)
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- Studies on the narciclasine alkaloids: Total synthesis of (+)- narciclasine and (+)-pancratistatin
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Enantioselective total syntheses of the antimmor alkaloids, (+)- narciclasine and (+)-pancratistatin, are reported. These syntheses feature a stereo- and regiocontrolled aryl enamide photocyclization to construct a common, advanced intermediate possessing a transfused BC substructure. Differential functional group interchange in the C-ring of this phenanthridone core structure allows for the production of the two target natural products in enantiomerically pure form.
- Rigby, James H.,Maharoof, Umar S. M.,Mateo, Mary E.
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p. 6624 - 6628
(2007/10/03)
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- Tellurolate-Induced 1,4-Elimination of 1,4-Dibromo-2-Enes. Syntheses of 1,3-Dienes
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Sodium 2-thienyltellurolate, generated in catalytic amounts from sodium borohydride and bis(2-thienyl) ditelluride, was found to efficiently debrominate 1,4-dibromo-2-olefins to 1,3-dienes under very mild reaction conditions.The required 1,4-dibromo-2-olefins were usually synthesized by allylic α,α'-bromination of olefins.Terminal olefins yielded, via allylic rearrangement, a mixture of 1,4-dibromo-2-olefins and 1,2-dibromo-3-olefins.Both these isomers were converted to 1,3-dienes (E/Z ca. 9/1) by the tellurolate reagent.The syntetic utility of the tellurolate-induced debromination reaction was demonstrated in a two-step synthesis of the main component of the red bollworm moth sex pheromone.
- Engman, Lars,Bystroem, Styrbjoern E.
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p. 3170 - 3174
(2007/10/02)
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- IMPROVED SYNTHESIS OF RACEMIC CHORISMIC ACID. CLAISEN REARRANGEMENT OF 4-EPI-CHORISMIC ACID AND DIMETHYL 4-EPI-CHORISMATE.
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The total synthesis of racemic chorismic acid (1) in eleven steps (6% overall yield) from methyl cyclohex-1-ene-4-carboxylate (9) is described. Dimethyl 4-epi-chorismate (8) and 4-epi-chorismic acid (6) are prepared by similar procedures, and their rate of Claisen rearrangement is investigated. A convenient preparation of disodium prephenate (2) and disodium 4-epi-prephenate (5) from dimethyl chorismate (7) and 8, respectively, is described.
- Hoare,Policastro,Berchtold
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p. 6264 - 6267
(2007/10/02)
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- High Pressure Experiments, XI. Reaction of Phosgene with 1,3-Cyclohexadiene at High Pressure
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Phosgene in toluene reacts at 80 deg C/5000 at with 1,3-cyclohexadiene to yield acyl chlorides.Without pressure no reaction is observed.After esterification the compounds 1-5 could be identified.The Diels-Alder adduct 6 was not observed.
- Kurz, Karlheinz,Plieninger, Hans
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p. 3666 - 3668
(2007/10/02)
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