Advanced organic reactions by Stuart W.

By Stuart W.

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Reduction of ketones to saturated hydrocarbons Zn(Hg), HCl H O Wolff-Kishner Reduction H Organic Reactions 1948, 4, 378 Comprehensive Organic Synthesis 1991, vol. 8, 327. - reduction of ketones to saturated hydrocarbons H2N-NH2, KOH H O H Radical Deoxygenation Review: Tetrahedron 1983, 39 , 2609 Chem. Rev. 1989, 89, 1413. Comprehensive Organic Synthesis 1991, vol. 8, 811 Tetrahedron 1992, 48, 2529 W. B. Motherwell, D. Crich Free Radical Chain Reactions in Organic Synthesis (Academic Press: 1992) - free radical reduction of halide, thio ethers, xanthates, thionocarbanates by a radical chain mechanism.

Substrate conc. solvent. 5 mol % Catalyst 50 : 1 150 : 1 33 : 1 52 : 1 OH REDUCTIONS 34 Olefin Isomerization: CH3 (3 : 1) OH OH olefin isomerization O OH major product - Conducting the hydrogenation at high H 2 pressures supresses olefin isomerization and often gives higher diastereoselectivity. Other Lewis basic groups can direct the hydrogenation. (Ir seems to be superior to Rh for these cases) OMe CO2Me OMe Ir CO2Me + Ir+ 99 : 1 O O CO2H Ir+ 7 : 1 Rh+ 1 : 1 O O N O O N O 130 : 1 1:1 Acyclic Examples Rh+ (2 mol %) OH Me CH 3 JCSCC 1982, 348 H2 (15 psi) Me L L M OH (97:3) H O OH H H Ph H 3C H H L CH3 Ph M L Ph anti H H O H 32 : 1 CO2H > 99 : 1 O > 99 : 1 Rh+ OH 1,2-strain Ph syn REDUCTIONS L L R3 H OH R3 35 H O M R2 R1 OH favored R3 H syn R1 R2 R1 R2 R3 H L H R1 R2 M OH disfavored R3 1,2-strain R1 R2 O H L anti - Supression of olefin isomerization is critical for acyclic stereocontrol !

Ed. Engl. 1978, 17, 569. ) Acid Chlorides O O O O N N + N R R OH R R N Cl + N N acyl pyridinium ion (more reactive) 1. SOCl2 2. PCl5 3. (COCl)2 Anhydrides O O P2O 5 2 R OH R O O R Activating Agents: Carbonyl Diimidazole O O O R OH N + N R N N N N Acyl Imidazole NH + CO + N PROTECTING GROUPS 63 Dicyclohexylcarbodiimide C 6H11 O NH O R + OH R N C N O O Nu: O C N R +C 6H11 Nu N H N H C 6H11 C 6H11 Ketene formation is a common side reaction- scambling of chiral centers C 6H11 O NH R R O C N H C O "ketene" C 6H11 Hydroxybenzotriazole (HOBT) - reduces ketene formation C 6H11 O R O N NH + O C N N N O N R N N OH C 6H11 N-Hydroxysuccinimide (NHS) O C 6H11 O R O O NH HO + O C N R N O N O C 6H11 O 2,2'-Dipyridyl Disulfide (Aldrithiol, Corey Reagent) Aldrichimica Acta 1971, 4 , 33 O R OH O Ph3P: + N S S R N + S + N N Ph3P=O SH Mukaiyama's Reagent (2-Chloro-1-methyl pyridinium Iodide or 2-Fluoro-1methyl pyridinium p-toulenesulfonate) Aldrichimica Acta 1987, 20 , 54 Chem.

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Advanced organic reactions by Stuart W.
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