- Methods for the synthesis of carbon-13 labelled acids and esters
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Syntheses of isotopically labelled putative biosynthetic intermediates to the natural products monocerin 1, hectochlorin 2 and strobilurin A 3 are described. For the preparation of [9,10-13C2] dihydroisocoumarin 10, a stereoselective aldol condensation of 13C2-acetylated chiral auxiliary 5 was used to assemble the labelled C9-C14 fragment. The preferred approaches to the syntheses of [1,2-13C2]5,5-dichlorohexanoic acid 15 and the N-acetylcysteamine derivative of [1,2-13C2]cinnamic acid 19 involved a Horner-Wadsworth-Emmons chain extension and Knoevenagel reaction, respectively. Copyright
- Jordan, Angela C.,Axford, Lorraine C.,Harding, John R.,O'Connell, Yvonne,Simpson, Thomas J.,Willis, Christine L.
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- An enantioselective synthetic route toward second-generation light-driven rotary molecular motors
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(Chemical Equation Presented) Controlling the unidirectional rotary process of second-generationmolecular motors demands access to these motors in their enantiomerically pure form. In this paper, we describe an enantioselective route to three new second-generation light-driven molecular motors. Their synthesis starts with the preparation of an optically active R-methoxy-substituted upper-half ketone involving an enzymatic resolution. The subsequent conversion of this ketone to the corresponding hydrazone by treatment with hydrazine led to full racemization. However, conversion to a TBDMS-protected hydrazone by treatment with bis-TBDMS hydrazine, prepared according to a new procedure, proceeds with nearly full retention of the stereochemical integrity. Oxidation of the TBDMS-protected hydrazone and subsequent coupling to a lower-half thioketone followed by recrystallization provided the molecular motors with >99% ee. As these are the first molecular motors that have a methoxy substituent at the stereogenic center, the photochemical and thermal isomerization steps involved in the rotary cycle of one of these new molecules were studied in detail with various spectroscopic techniques.
- Pijper, Thomas C.,Pijper, Dirk,Pollard, Michael M.,Dumur, Frederic,Davey, Stephen G.,Meetsma, Auke,Feringa, Ben L.
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- Practical Procedures for the Preparation of N-tert-Butyldimethylsilylhydrazones and Their Use in Modified Wolff-Kishner Reductions and in the Synthesis of Vinyl Halides and gem-Dihalides
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In this work we develop practical chemistry for the preparation of N-tert-butyldimethylsilylhydrazone (TBSH) derivatives from carbonyl-containing compounds and show that these products serve as superior alternatives to simple hydrazones in Wolff-Kishner-type reduction reactions, in the Barton vinyl iodide preparation, in the synthesis of vinyl bromides, and in the synthesis of gem-diiodides, gem-dibromides, and gem-dichlorides. In our new procedure for silyl hydrazone synthesis, aliphatic and aromatic ketones and aldehydes are shown to undergo highly efficient coupling (typically >95% yield) to form the corresponding TBSH derivatives when combined with equimolar amounts of 1,2-bis(tert-butyldimethylsilyl)-hydrazine (BTBSH) and a catalytic quantity of scandium trifluoromethanesulfonate (typically, 0.01 mol %), neat, or in solvent. Optimized procedures are provided for the use of TBSH derivatives in a Wolff-Kishner-type reduction protocol that proceeds at low temperature (23-100 °C) and in a single reaction flask. Similarly, protocols for the use of TBSH derivatives as precursors to vinyl halides and gem-dihalides are described in detail.
- Furrow, Michael E.,Myers, Andrew G.
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p. 5436 - 5445
(2007/10/03)
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