Tert Butyl acetate, hydrolysis

Prior to the actual metathesis event, coupling of 13 and 28 via an ester linkage was required (Scheme 2.3). Two methods were employed in this connection. The first involved the aforementioned two-carbon expansion of aldehyde 28. Thus, condensation of 28 with Rathke anion (lithiated tert-butyl acetate) generated a mixture of dia-stereomeric alcohols the major product was shown to have the requisite 3S configuration. TBS protection of ester 29 and subsequent ester hydrolysis generated the desired add, 31, which could be further esterified with alcohol 13 in 78 % yield. 

Positive-Tone Photoresists. The ester, carbonate, and ketal acidolysis reactions which form the basis of most positive tone CA resists are thought to proceed under specific acid catalysis (62). In this mechanism, illustrated in Figure 22 for the hydrolysis of tert-butyl acetate (type A l) (63), the first step involves a rapid equilibrium where the proton is transferred between the photogenerated acid and the acid-labile protecting group ... 

Figure 7. Rate profiles for acetate hydrolysis. Type I methyl acetate, type II sec-butyl acetate, t5rpe III phenyl acetate, t3rpe IV tert-butyl acetate. (Reprinted from Ref. 110 with permission of the American Chemical Society.)...

The catalytic hydrolysis of tert-butyl acetate in water is characterized by the following parameters ... 

The most frequently encountered hydrolysis reaction in drug instability is that of the ester, but curtain esters can be stable for many years when properly formulated. Substituents can have a dramatic effect on reaction rates. For example, the tert-butyl ester of acetic acid is about 120 times more stable than the methyl ester, which, in turn, is approximately 60 times more stable than the vinyl analog [16]. Structure-reactivity relationships are dealt with in the discipline of physical organic chemistry. Substituent groups may exert electronic (inductive and resonance), steric, and/or hydrogen-bonding effects that can drastically affect the stability of compounds. A detailed treatment of substituent effects can be found in a review by Hansch et al. [17] and in the classical reference text by Hammett [18]. 

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

Substituted oxazolidin-5-one derivatives, which are prepared from N -protected a-annino dicarboxyhc acids and paraformaldehyde, are employed for dual protection of the a-annino and a-carboxy groups in the synthesis of P-aspartyl and y-glutamyl esters (Scheme 4).Py For this purpose the oxazolidinone derivatives are synthesized by treatment of the Z amino acids with paraformaldehyde in a nnixture of acetic anhydride, acetic acid, and traces of thionyl chloride or by azeotropic distillation of the Z amino acids with paraformaldehyde and 4-toluenesulfonic acid in benzene. The resulting heterocychc compounds are readily converted into the tert-butyl esters with isobutene under acid catalysis. Esterification is achieved with tert-butyl bromidet or with Boc-F.P l Finally, the oxazolidinone ring is opened by alkaline hydrolysis or catalytic hydrogenolysis to yield the tert-butyl esters. 

In 2005, Ramachandran and coworker reported the asymmetric methylation of tert-butyl 2-(6-methoxynaphthalen-2-yl)acetate (67) using cinchoninium PTC 69 and strong base potassium fert-butoxide (Scheme 6.20) [45], The optically active methylated product 68 can be converted to naproxen, a nonsteroidal anti-inflammatory drug, by hydrolysis of ester. 

Kinetic resolution of ( ) diethyl 2,3-epoxypropylphosphonate by enantioselective hydrolysis has recently been described (Scheme 4.50). In the presence of (7 ,7 )-MA -(>w(3.5-di-tert-butyl-salicylidene)-l,2-cyclohexanediaininocobalt(lll) acetate and H2O for 19 h, racemic diethyl 2,3-epoxpropylphosphonate is converted into a mixture of (S )-)-) diethyl 2.3-epoxypropylphosphonate (82% ee) and diethyl (/ )-(-) 2,3-dihydroxypropylphosphonate (98% ee). An improved enantiomeric excess (93% ee) of (S)-(-) diethyl 2,3-epoxypropylphosphonate has been obtained after a 72-h hydrolytic kinetic resolution experiment.-" ... 

A new type of copolymer resist named ESCAP (environmentally stable chemical amplification photoresist) has recently been reported from IBM [163], which is based on a random copolymer of 4-hydroxystyrene with tert-butyl acrylate (TBA) (Fig. 37), which is converted to a copolymer of the hydroxystyrene with acrylic acid through photochemically-induced acid-catalyzed deprotection. The copolymer can be readily synthesized by direct radical copolymerization of 4-hydroxystyrene with tert-butyl acrylate or alternatively by radical copolymerization of 4-acetoxystyrene with the acrylate followed by selective hydrolysis of the acetate group with ammonium hydroxide. The copolymerization behavior as a function of conversion has been simulated for the both systems based on experimentally determined monomer reactivity ratios (Table 1) [164]. In comparison with the above-mentioned partially protected PHOST systems, this copolymer does not undergo thermal deprotection up to 180 °C. Furthermore, as mentioned earlier, the conversion of the terf-butyl ester to carboxylic acid provides an extremely fast dissolution rate in the exposed regions and a large... 

BOC-(D-Phe)2-OMe was synthesized with 78% yield by using isobutyl chloroformate and triethylamine, from BOC-D-Phe which had been prepared from D-phenylalanine, BOC-ON and D-phenylalanine methylester. BOC-(D-Phe)4-OMe was synthesized with water soluble carbodiimide (WSCI) with 84% yield from BOC-(D-Phe)2 prepared by alkaline hydrolysis of BOC-(D-Phe)2-OMe and (D-Phe)2-OMe prepared from BOC-(D-Phe)2-OMe by removing the BOC group in 4N-HCl/ethyl acetate. (D-Phe)4 HCl was synthesized similarly with 80% yield from BOC-(D-Phe)4-OMe, first by alkaline hydrolysis and then by removal of the BOC group. Similarly, the following peptide derivatives were synthesized to characterize the enzyme Boc-D-Phe, D-Phe tert-butyl ester, (D-Phe)2 HCl, Boc-(D-Phe)2, (D-Phe)2 methyl ester-HCl, Boc-(D-Phe)2 methyl ester, (D-Phe)3-HCl, Boc-(D-Phe)3, Boc-(D-Phe>3 methyl ester, Boc-(D-Phe>3 tert-butyl ester, (D-Phe)4-HCl, Boc-(D-Phe)4, Boc-(D-Phe>4 methyl ester, L-... 

The hydrolysis rate of the ester depends on its chemical structure. The rates of alkaline hydrolysis of isobutyl and butyl acetates are greater at room temperature than that of icc-butyl acetate cr/-butyl acetate is even more stable under alkaline conditions (iso x n > sec tert). The rates of acid hydrolysis of the butyl acetates decrease in the order iso > n> ten > sec. 

Acid hydrolysis of fert-butyl acetate in 0-labeled water was found to give tert-butyl alcohol having an content nearly identical to that of the solvent. Suggest a mechanism consistent with this observation. (It was shown that incorporation of into tert-butyl alcohol after it was formed did not occur.)... 

Asaad, N. and Engberts, J.B.F.N., Cytosol-mimetic chemistry kinetics of the trypsin-catalyzed hydrolysis of p nitrophenyl acetate upon addition of polyethylene glycol and n-tert-butyl acetoacetamide, /. Am. Chem. 

Preparation by oxidation of 7-tert-butyl-2,3-diphenyl-benzofuran with chromium trioxide in acetic add at 70° for 2 h, followed by alkaline hydrolysis of the keto ester obtained (2-benzoyloxy-3-tert-butylbenzophenone) in boiling diluted ethanol for 15 min [717]. 

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