Base Sensitivity

Ether solution of Zn(BH4)2 is neutral- good for base sensitive compounds... 

Note 1. No cyanide was used to remove the copper salts, since the nitrile is probably very base-sensitive (isomerization to a conjugated diene). 

General note. The propargyl ketone is extremely base-sensitive. Traces of alkali... 

APA may be either obtained directly from special Penicillium strains or by hydrolysis of penicillin Q with the aid of amidase enzymes. A major problem in the synthesis of different amides from 6-APA is the acid- and base-sensitivity of its -lactam ring which is usually very unstable outside of the pH range from 3 to 6. One synthesis of ampidllin applies the condensation of 6-APA with a mixed anhydride of N-protected phenylglydne. Catalytic hydrogenation removes the N-protecting group. Yields are low (2 30%) (without scheme). 

Because primary and secondary alkyl hydroperoxides are base-sensitive they are converted to peroxyesters by reaction with a ketene or by the reaction of their barium salts with acid chlorides (44). 

Bu4N F , THF, 25°, 1 h, >90% yield. Fluoride ion is very basic especially under anhydrous conditions and thus may cause side reactions with base-sensitive substrates. ArOTBDMS ethers can be cleaved in the presence of alkyl OTBDMS ethers. ... 

KCN, 95% EtOH, 20° to reflux, 12 h, 93% yield.Potassium cyanide is a mild transesterification catalyst, suitable for acid- or base-sensitive compounds. When used with 1,2-diol acetates hydrolysis proceeds slowly until the first acetate is removed. ... 

Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The ethers are stable... 

These neutral conditions can be used to prepare thiol esters of acid- or base-sensitive compounds including penicillins. ... 

The ester, formed from the acid (COCE, toluene then CH2=CHCH2CH20H, acetone, —78° warm to rt, 70-94% yield), can be cleaved by ozonolysis followed by Et3N or DBU treatment (79-99% yield), the ester is suitable for the protection of enolizable and base-sensitive carboxylic acids. ... 

The procedures presented here are simple, Inexpensive, and may be used on a large scale. The use of potassium hydroxide In this reaction may, however, prove Incompatible with certain base-sensitive functional groups. 

A variety of conditions has been used to prepare oxiranes from trans-hxomo-hydrins. In general, bromohydrins are heated in a solution of 5-10% methanolic potassium hydroxide for 30 min to 8 hr. Longer reflux times are required for bromohydrins which are not anti-coplanar, e.g., diequatorial bromohydrins. A 5 % solution of potassium acetate in boiling ethanol can be used to cyclize steroidal bromohydrins containing base sensitive groups. The use of 1.1 equivalents of sodium methoxide per equivalent of steroid in methanol solution is especially recommended for 9a-bromo-l lj5-hydroxy steroids. 

The use of lithium acetylide in tetrahydrofuran has recently been recommended for base-sensitive 17-keto steroids, ... 

Hydrolysis of the intermediate epoxy acetate is generally carried out with strong alkali if base-sensitive groups are present, milder conditions (e.g., potassium bicarbonate, potassium carbonate) can be employed. If commercial peracetic acid (which contains sulfuric acid) is used for epoxidation, the intermediate epoxy acetate cannot be isolated, but is hydrolyzed in situ by the acid to the desired ketol. Acid hydrolysis will also retain 3-acetates, if present. ... 

Dehydrofluorination by primary and secondary aliphatic amines occurs at room temperature and is the basis of diamine cross linkmg, which occurs by dehydrofluonnation and subsequent nucleophihc substitution of the double bond The locus of dehydrofluonnation is a VDF unit flanked by two perfluoroolefin units This selectively base-sensitive methylene group also undergoes elimination as the first step in phase-transfer-catalyzed cross-hnking with quaternary ammo mum or phosphomum salts, bisphenols, and morganic oxides and hydroxides as HF acceptors [31, 32]... 

Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The ethers are stable to Grignard and Wittig reactions and to reduction with lithium aluminum hydride at —15°. Aryl -butyldimethylsilyl ethers and other sterically more demanding silyl ethers require acid- or fluoride ion-catalyzed hydrolysis for removal. Increased steric bulk also improves their stability to a much harsher set of conditions. An excellent review of the selective deprotection of alkyl silyl ethers and aryl silyl ethers has been published. ... 

Thermitase, pH 7.5, 55°, 50% DMSO, 3-140 min. This method was used to avoid the degradation of base-sensitive side chains during peptide synthesis. The method is compatible with the Fmoc group. ... 

These base-sensitive protective groups were introduced from the chloroformate or azidoformate. They are more sensitive to base than is the Fmoc group. Cleavage times with 0.2 mL of piperidine to 0.1 mmole of urethane in 5 mL of CHCL at It occur as follows Climoc, <10 min Bimoc, <14 h Fmoc, 18 h. °... 

I Secondary alcohols are oxidized by a variety of reagents to give ketones (Section 17.8). The choice of oxidant depends on such factors as reaction scale, cost, and acid or base sensitivity of the alcohol. 

These reagents exhibit a high selectivity for the attack of aldehydic over ketonic oxo groups26. The triethylammonium salt of 2-(bromomethyl)acrylic acid and base-sensitive aldehydes, under these conditions, can be used for the synthesis of lactones27. 

Based on the kinetic studies, a mechanism for this oxidation was proposed45 which involves a nucleophilic attack by the sulphide on a cyclic hydrogen-bonded form of the peracid (equation 9). Since oxidation using peracids occurs under very mild conditions, it can be successfully applied to the preparation of base sensitive sulphoxides. Thus, di(a-bromobenzyl) sulphoxide 25, which is very labile in the presence of a base, was obtained by careful oxidation of a-di(a-bromobenzyl) sulphide by means of m-chloroperbenzoic acid (MCPBA)46 (equation 10). 

Trost published a desulphonylation procedure for aryl alkyl sulphones using an excess of sodium amalgam in buffered ethanol126 (equation 52). Trost claimed that this is superior to earlier reactions using sodium amalgam in ethanol because of a couple of factors the use of the acid phosphate buffer to prevent formation of significant amounts of sodium methoxide is particularly important, since this can cause isomerizations in base-sensitive substrates, and the temperature should be kept low, but optimized for each substrate. 

Dixon B (2005) Applicability of neuro-ftizzy techniques in predicting ground-water vulnerability a GIS-based sensitivity analysis. J Hydrol 309 17-38... 

Bismuth(III) triflate is also a powerful acylation catalyst that catalyzes reactions with acetic anhydride and other less reactive anhydrides such as benzoic and pivalic anhydrides.113 Good results are achieved with tertiary and hindered secondary alcohols, as well as with alcohols containing acid- and base-sensitive functional groups. 

The reaction in Entry 5 is a case in which the thermal conditions were preferable to the basic conditions because of the base sensitivity of the product. Entries 6 to 10 show anionic oxy-Cope reactions. Entries 6 and 7 are early examples of the application of the reaction in synthesis. Entries 8 and 9 involve rearrangements of bicyclo[2.2.1]hept-2-en-2-ol derivatives to give cw-fused bicyclo[4.3.0]non-7-en-3-ones. 

If total analysis systems are not exactly the best option for polymer/additive analysis, then neither are chip-based hyphenations. The reasons here are completely different minute sample size (homogeneity problems for more traditional samples), and (theoretical) limits to chromatography and concentration-based sensitivity, etc. 

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