Transesterification tert-butyl esters

The boronic acid ester B was synthesized by transesterification of the corresponding pinacolester A with (lR,2R)-l,2-dicyclohexyl-l,2-dihydroxyethane. Stereoselective chlorination of B was carried out with (dichloromethyl) lithium and zinc chloride. Reaction of the obtained chloroboronic ester C with lithio 1-decyne followed by oxidation of the intermediate D with alkaline hydrogen peroxide afforded the propargylic alcohol E. Treatment with acid to saponify the tert-butyl ester moiety and to achieve ring closure, produced lactone F. Finally, Lindlar-hydrogenation provided japonilure 70 in an excellent yield and high enantiomeric purity. 

The classical method for tert-butyl esterification involves nnineral add catalyzed addition of the amino acid to isobutene. Both, N-protected, e.g. Z-Xaa-OH, and unprotected amino acids form tert-butyl esters with isobutene in the presence of catalytic amounts of sulfuric acid or TosOH. " Another efficient method is the transesterification of an acetic acid tert-bvXy ester catalyzed by perchloric acid. " Amide tert-butylation was recognized as a side reaction in the presence of perchloric acid, but could be completely suppressed by using sulfuric acid. Both methods, acid-catalyzed addition to isobutene and the transesterification of acetic add terf-butyl esters, result in simultaneous terf-butyl-ation of hydroxy and sulfanyl groups. A synthetic route to Z-Thr-OtBu, Z-Ser-OtBu, and Z-Hyp-OtBu without conconnitant O-alkylation involves the hydroxy protection by the acetoacetyl group, which is readily cleaved by treatment with 2 equivalents of hydrazine in EtOH for 30 minutes. ... 

In the case of acid catalysis or transesterification, it is possible to push the reaction to the right by removal of water (azeotropic distillation) or the volatile methanol. Alternatively, preparation of the tert-butyl ester confers resistance to alkali, but allows removal of the protecting group under mildly acidic conditions. The ester, which for steric reasons cannot be prepared from fert-butanol, may be synthesized from isobutylene gas in the presence of acid, or by transesterification with ferf-butyl acetate. 

There are very few known methods, for transesterifications using bulky alcohols. Thiol esters undergo ready mercury(II) trifluoroacetate-catalyzed transesterifications with tert-butyl alcohol. Potassium tert-butoxide in the... 

The synthesis of long-chain fatty acid esters of carbohydrates is inherently more demanding. It was found that glucose did not react with vinyl laurate in a pure ionic liquid medium, but in biphasic tert-butyl alcohol/[BMIm][PF6], glucose could be acylated by the vinyl esters of O, 2-Cu, fatty acids. The best results were obtained with CaLB, which was twice as active as TIL, and the selectivity for acylation at C-6 was high [114]. The esterification of glucose with palmitic acid, which is, in an industrial context, to be preferred over transesterification, has recently been demonstrated in tert-butyl alcohol/[BMIm][PF6] medium [115]. 

Common synthetic methods for the preparation of cyclic 8-enamino esters are the condensation between a lactim ether and benzyl cyanoacetate followed by hydrogenolytic decarboxylation, or the imino ester carbon-carbon condensation with tert-butyl cyanoacetate followed by a trifluoroacetic acid treatment. The use of a thiolactam condensed with ethyl bromoacetate gives, after sulfur extrusion by triphenylphosphine, cyclic 8-enamino esters. Compared with these methods, the Meldrum s acid condensation followed by the monodecarboxylating transesterification described here is more convenient and practical. An extension of this procedure permits preparation of smaller... 

Due to the instability of the feri-butyl ester, and the resistance of the ethyl ester to transesterification, installation of the methyl ester prior to glycosylation was clearly required. Conversion of tert-butyl enol ester 51b to the methyl ester 51a was achieved in 78% yield over two steps, with hydrolysis of the tert-bvAy ester using trifluoroacetic acid at 0 °C, followed by methylation with trimethylsilyl diazomethane (Scheme 21). Gratrfyingly, when methyl enol ester 51a was... 

In the mixture of secondary alcohol or primary alcohol with tertiary esters, the products of secondary alcohol esters or primary alcohol esters would be further chemically combined immediately. A hydrogen atom in the raw esters would react with a-carbon atom to form alcohols, which would not be oxidized. Transesterification reaction would happen for tert-butyl nitrite because of the instability of NO. 

Vinyl-functional alkylene carbonates, useful in the preparation of polymers that contain alkylene carbonate pendant groups, can also be prepared from GC. Two examples are the reaction of GC with maleic anhydride and acryloyl chloride to produce the acrylate-functional cyclic carbonates (3 and 4, respectively. Scheme 24). Although the transesterification of alkyl esters such as dimethyl maleate or methyl acrylate by reaction with GC represents an obvious means of obtaining the above materials, the temperatures required of such processes (>100°C) result in unwanted polymerization of both the reactant and product species, even in the presence of well-known radical inhibitors such as 2,6-di-tert-butyl-p-cresol or phenothiazine. In addition, the synthesis of vinyl-functional alkylene carbonates is greatly complicated by the fact that such materials cannot be purified by distillation and must be stored at temperatures < 0 ° C in the presence of a... 

Theil et al. developed a method for chemoenzymatic synthesis of both enantiomers of cispentacin [89]. frans-2-Hydroxymethylcyclopentanol, obtained by the sodium borohydride reduction of ethyl 2-oxocyclopentanecarboxylate, was monosilylated with tert-butyldimethylsilyl (TBDMS) chloride to afford 55. Lipase PS-catalysed transesterification with vinyl acetate in /erf-butyl methyl ether furnished the ester 56 and the alcohol 57. The deacetylated 58 was obtained by the Mitsunobu reaction with phthalimide, triphenylphosphine and diethyl azodicarboxylate (DEAD) to furnish the cis oriented 59 with inversion of configuration (not retention as mentioned in the original article) (Scheme 9). Desilylation, Jones oxidation and subsequent deprotection with aqueous methylamine gave the ( R,2S) enantiomer 5 [89]. The (15, 2/f) enantiomer was prepared by the same route from the silyl alcohol 57. 

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