Transesterification transetherification

Covalent polymers with reversible properties arising from dynamic covalent bonds such as disulfide exchange reaction [47 9], transesterification [50,51], transetherification [52], and boronate ester formation [53] were reported without respect to DCC. These studies should involve DCLs in... 

Hydrolysis of carboxylic esters 0-17 Transetherification 0-18 Payne rearrangement 0-23 Transesterification 0-55 Ammonolysis of carboxylic esters 0-68 Cleavage of ethers with concentrated acids... 

Enol Ethers and Esters 0-15 O-Alkylation of carbonyl compounds with diazo alkanes 0-17 Transetherification 0-20 Reaction between acyl halides and active hydrogen compounds 0-23 Transesterification 0-24 Acylation of vinylic halides 0-94 Alkylation with ortho esters 0-107 O-Acylation of 1,3-dicarbonyl compounds... 

Tosylation (see also Sulfonylation) /7-Toluenesulfonyl chloride, 313 Transesterification f-Butyldimethylsilyl trifluoromethanesul-fonate, 50 Butyllithium, 56 Transetherification Bromodimethylborane, 47 Transmetallation Butyllithium, 319... 

The method of transetherification or the related transesterification should be applicable to other dendrimer polymer systems. Transamidation has been performed with poly(propylene imine) dendrimer and poly(e-caprolactone). The linear chain is fragmented according to Scheme 19b, and a mixture of star and linear polymer is formed [135]. The average MW of the arms is equal to the MW of the linear fragments. 

Transetherification and transesterification. Tin(II) bromide is a catalyst for converting p-methoxybenzyl ethers into methoxymethyl ethers by CH2(OMe)2 and MeOCH2Br. Benzyl ethers and trimethylsilyl ethers are cleaved and acetylated in one operation by the action of SnBr2-AcBr in CH2CI2 at room temperature. 

Many monoterpenes are desired fragrances in perfumery and flavors in food. They are produced on a larger scale from acetone (C3) and ethyne (acetylene C2) involving repetitive synthetic steps (Fig. 5). Initially, acetone is ethynylated by acetylene in the presence of a base (sodium hydroxide, amines with sodium carbonate) yielding 3-butyn-2-ol (C5) which is partially hydrogenated in the presence of deactivated catalysts (Lindlar catalysts) to 2-methyl-3-buten-2-ol. This can be converted to the key intermediate 6-methyl-5-hepten-2-one (Cg) via two pathways, either by transetherification with methylpropenylether and subsequent oxa-CoPE rearrangement, or by transesterification with methyl acetoacetate and subsequent Carroll decarboxylation. 

Enol ethers are prepared by acid-catalyzed transesterification or transetherification from other enol ethers, orthoesters, ketone acetals and similar precursors with allyl alcohol. The intermediate isopyrocin (the same holds for pyrocin) [48] is cleaved with thionyl chloride to afford the substrate 35 for cyclizing 1,3-elimination (Reaction scheme 21) in the presence of base [49] without significant P-elimination. 

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