Protection selection

The a-naphthyldiphenylmethyl ether was prepared to protect, selectively, the 5 -OH group in nucleosides. It is prepared from a-naphthyldiphenylmethyl chloride in pyridine (65% yield), and cleaved selectively in the presence of a p-methoxy-phenyldiphenylmethyl ether with sodium anthracenide, a (THE, 97% yield). The p-methoxyphenyldiphenylmethyl ether can be cleaved with acid in the presence of this group. 

PhN=C=0, Pyr, 20°, 2-3 h, 100% yield. This method was used to protect selectively the primary hydroxyl group in several pyranosides. ... 

ClCH20Me, CH2CI2, NaOH-H20, Adogen (phase-transfer cat.), 20°, 20 min, 80-95% yield. This method has been used to protect selectively a phenol in the presence of an alcohol. ... 

This approach to carbonyl protection uses the relative differences in the basicity and the differences in steric effects to protect selectively either the more basic... 

Phthalimide-NC02Et, aq. Na2C03, 25°, 10-15 min, 85-95% yield. This reagent can be used to protect selectively primary amines in the presence of secondary amines. ... 

Purpose Unfavourable operating conditions Fault conditions Protection Single-device motor protection relays Summary of total motor protection Motor protection by thermistors Monitoring of a motor s actual operating conditions Switchgears for motor protection Selection of main components Fuse-free system... 

Bu2SnO, benzene BnBr, DMF, heat, 80% yield. This method has also been used to protect selectively the anomeric hydroxyl in a carbohydrate derivative. The replacement of Bu2SnO with Bu2Sn(OMe)2 improves the process procedurally. The use of stannylene acetals for the regioselective manipulation of hydroxyl groups has been reviewed. ... 

HCOOH, 60°, 1 h, 93% yield. This method can be used to protect selectively only the primary alcohol of a pyranoside. ... 

Bu2SnO, toluene, reflux, 4 h Pd(Ph3P)4, THE, CH2=CHCH(OAc)2, rt, 1 h, 80-89% yield. In pyranoside protection, selectivity for 1,3-dioxane formation is generally observed, but dioxolanes are often formed. 

PhCHO, CHCI3, 3A molecular sieves NaBH4 alcohol solvent, 66% yield. These conditions were used to protect selectively the terminal ends of a polyamine. ... 

Just as certain pyranose sugars can give rise to bis-acetal or bis-ketal derivatives which constitute linearly fused 5 6 6 systems (cf. Section 12.17.2.1.7), another set of bis-acetals and bis-ketals - in many cases derived from the same sugars - correspond to angularly fused 5 6 6 systems. These, like their linearly fused analogues, serve to protect, selectively, four hydroxyl groups of the parent sugars, and cyclic carbonates (l,3-dioxolan-2-ones) may fulfill similar functions. 

Aldehydes are more reactive than ketones. Therefore, aldehydes react with ethylene glycol to form acetals preferentially over ketones. Thus, aldehydes can be protected selectively. This is a useful way to perform reactions on ketone functionalities in molecules that contain both aldehyde and ketone groups. 

Nouguier first developed a new method to protect selectively the sugars at the primary alcohol function, using the conventional agent dihydropyran... 

Over Hid new experiments selected from the literature to illustrate new reagents and techniques, and the operation of protection, selectivity and control in synthesis. 

Hardenbol, P. and van Dyke, M.W. (1996) Sequence specificity of triplex DNA formation analysis by a combinatorial approach, restriction endonuclease protection selection and amplification. Proc. Natl. Acad. Sci. USA, 93, 2811-2816. 

With TBSC1 a primary alcohol can be protected selectively in presence of secondary ones. 

Benzylidene and isopropylidene acetals are often used for the selective protection 1,2-cis or 1,3-cisjtrans diols of sugar derivatives. They are stable to strong basic conditions but quite fragile towards acid. Recently, dispirodiketal and cyclohexane-1,2-diacetal groups have been introduced to protect selectively 1,2-trans diols of carbohydrates. 

In reactions involving oxygen and hydrocarbons, the catalyst surface is necessarily reduced to some extent, due to the steady-state occurrence of reduction and reoxidation processes. The above results suggest that ideally, the surface should be as dose as possible to full oxidation. The main objective of the present contribution is to understand why donors of spillover oxygen can keep the surface in a higher oxidation state and thus protect selective sites on the surface and prevent the decay of catalysts to form segregated phases... 

Bu2SnO, benzene BnBr, DMF, heat, 80% yield.12 This method has also been used to protect selectively the anomeric hydroxyl in a carbohydrate derivative.13... 

Personnel protective equipment may be used in certain circumstances where exposure to airborne particulates contaminated with chemical carcinogens could occur. In those situations, personnel should be equipped with a complete clothing change, as well as respiratory protection selected on the basis of work performed, type of chemical used, and containment equipment. The respiratory protection may be a face mask, respirator [selected from those approved by the National Institute for Occupational Safety and Health (NIOSH)] (4, 5), or emergency breathing air system. In the latter case, a head hood or a complete protective suit may be used with a breathing air supply system. Figure 2. 

The presence of an a, -conjugated double bond noticeably reduces the electrophilic activity of a carbonyl carbon. This effect allows one to protect, selectively, an isolated keto group as a ketal in the presence of a conjugated enone moiety. Thus, the selective transformations of conjugated enones, a situation frequently encountered in steroid chemistry, are achieved in this manner. 

Compound 13p is treated with methanesulfonyl chloride in methylene chloride in presence of triethylamine to provide mesyl derivative 13q in which the three hydroxylic fiinctions at C-3, C-4 and C-5 have been protected selectively with three different groups. 

Safety from potential dust cloud explosions could include taking measures to avoid an explosion (explosion prevention) or designing plant and equipment so that in the event of an explosion people and plant are protected (explosion protection). Selection of... 

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