Oxidation leaving group generation

Reaction of pyridine N-oxide 860 with excess allyltrimethylsilane 82 affords, via 947, 2-propenylpyridine 948 in 53% yield as the only reaction product which can be isolated. Ehmination of trimethylsilanol 4 from 947 is apparently followed by fluoride-catalyzed isomerization of 2-allylpyridine into 2-propenylpyridine 948. 3-Methylpyridine-N-oxide 867 a is converted into 2-propenyl-3-methylpyridine in 69% yield. Likewise, fluoride-catalyzed addition of excess benzyltrimethylsilane 83 to 860 furnishes, via 949, 2-benzylpyridine 950 in 70% yield. The generated leaving group trimethylsilanol 4 reacts with excess allyltrimethylsilane 82 or benzyltrimethylsilane 83 in the presence of fluoride to give hexamethyldisiloxane (HMDSO) 7 and propylene or toluene, respectively [60] (Scheme 7.16). 

Actually, nitronates are the closest related derivatives of nitronic acids, that is, aci forms of AN, which exist in labile equilibrium with true AN. Some derivatives of nitronic acids, —CH=N(0)0X, where OX is the good leaving group, are evident intermediates in the most well-developed procedures for the synthesis of nitrile oxides from primary AN. In this chapter, special emphasis is given to particular nitronates, which are generated from a-functionalized AN and can also be considered as precursors of a-functionalized nitrile oxides. 

The nitrolysis of tertiary amines in the form of fert-butylamines and methylenediamines has been used to synthesize numerous polynitramine-based energetic materials. In these reactions one of the N-C bonds is cleaved to generate a secondary nitramine and an alcohol the latter is usually 0-nitrated or oxidized under the reaction conditions (Equation 5.15). The ease in which nitrolysis occurs is related to the stability of the expelled alkyl cation. Consequently, the fert-butyl group and the iminium cation from methylenediamines are excellent leaving groups. 

The leaving group is the enolate anion of acetyl-CoA, and the reaction thus cleaves off a two-carbon fragment from the original fatty acyl-CoA. Since the nucleophile is coenzyme A, the other product is also a coenzyme A ester. In fact, the reaction generates a new fatty acyl-CoA, shorter by two carbons, which can re-enter the P-oxidation cycle. Most natural fatty acids have an even number of carbons, so the process continues until the original fatty acid chain is cleaved completely to acetyl-CoA fragments. 

Sometimes, when a Swern oxidation produces a carbonyl compound possessing a good-leaving group at the 3-position, an in situ elimination occurs, resulting in the generation of a conjugated enone or enal. 

Other leaving groups are effective in the oxidative addition with Pd , and can lead to efficient Heck reactions. An attractive possibihty is an aniline as starting material, with in situ generation of a diazonium salt. While the oxidation of the amino group can occur with Pd° alone at elevated temperatures, dehberate addition of t-butyl nitrite leads to... 

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