Module I Oxidation Reactions - NPTel

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NPTEL – Chemistry – Reagents and Organic reactions The reactions are generally carried out in a mixture of tert-butyl alcohol and water at ambient temperature (Scheme 12). Features: Me Me Me Me O O H H Me Me AD-mix t-BuOH-H 2O AD-mix t-BuOH-H 2O AD-mix t-BuOH-H 2O Scheme 12 Joint initiative of IITs and IISc – Funded by MHRD Page 6 of 122 HO Me Me O OH Me Me O H Me OH OH H Me OH The reaction is stereospecific leading to 1,2-cis-addition of two OH groups to the alkenes It typically proceeds with high chemoselectivity and enantioselectivity The reaction conditions are simple and the reaction can be easily scaled up The product is always a diol derived from cis-addition. It generally exhibits a high catalytic turnover number It has broad substrate scope without affecting the functional groups OH
NPTEL – Chemistry – Reagents and Organic reactions 1.1.4 Aminohydroxylation Similar to cis-1,2-dihydroxylation, cis-1,2-aminohydroxylation of alkenes has been developed by reaction with chloroamine in the presence of catalytic amount of OsO4. In this process, alkene reacts with chloroamine in the presence of OsO4 to give sulfonamides that is readily converted into the cis-1,2-hydroxyamines by cleavage with sodium in liquid ammonia (Scheme 13). This process provides a direct cis-aminohydroxylation of alkenes, but the major problem is the poor regioselectivity for unsymmetrical alkenes. R R' Mechanism K 2OsO 2(OH) 4 Ts-N(Na)Cl, H 2O-t-BuOH K 2OsO 2(OH) 4 Ts-N(Na)Cl, H 2O-t-BuOH TsHN Joint initiative of IITs and IISc – Funded by MHRD Page 7 of 122 R Scheme 13 R' OH OH NHTs Na/liq. NH 3 Na/liq. NH 3 The catalytically active species in the reaction most likely is an imidotrioxo osmium(VIII) complexes, which is formed in situ from the osmium reagent and the stoichiometric nitrogen source, i.e. chloroamine (Scheme 14). Experiments under stoichiometric conditions have been shown that imidotrioxo osmium(VIII) complexes transfer the nitrogen atom and one of the oxygen atoms into the substrate. The major regioisomer normally has the nitrogen placed distal to the most electron withdrawing group of the substrate. O Os O O NX + R R R O O Os O N X R Scheme 14 R O O Os NX O R H 2O H 2N R HO R XHN R' OH OH NH 2 R
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Module I Oxidation Reactions - NPTel

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