Group selectivity

Functional group selectivity is often easy to achieve in reduction and condensation reactions since several highly selective reagents for reduction and for protection offunctional groups are available. 

Donors a.ndAcceptors. Table 3 Hsts common electron—donor groups, and electron—acceptor groups selected from a large number capable of evoking fluorescence. 

Ph) or OPh, the last two of which may be substituted by up to three groups selected from alkyl, alkoxy, sulfonate, carboxylate, alkylthio-,... 

Aminophenols. Reaction of chloroformate with aminophenols (qv) also takes place at the more reactive amino group selectively. Thus (9-aminophenol [95-55-6] gives benzoxazolone [59-49-4] by cyclization of the intermediate carbamate (31). 

It is possible to introduce this group selectively onto a primary alcohol in the presence of a secondary alcohol. The derivative is stable to KMn04, w-chloro-peroxybenzoic acid, LiAlH4, and Cr03 Pyr. Since this derivative is similar to the p-methoxyphenyl ether it should also be possible to remove it oxidatively. The GUM ethers are less stable than the MEM ethers in acid but have stability comparable to that of tlie SEM ethers. It is possible to remove the GUM ether in the presence of a MEM ether. 

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DDQ, CH3CN, H20. These conditions normally cleave the PMB group selectively in the presence of a TBDMS group. ... 

In view of the unexpected effects of the C-2 and C-3 substituents on the reaction of C-4 sulfonates, it is worthwhile to point out the observations made with some 2,3-dideoxy derivatives. Treatment of ethyl 2,3-dideoxy-4,6-di-0-methylsulfonyl-D-ert/ hro-hexopyranoside (40) with sodium iodide and acetone at 115°C. caused the displacement of the C-6 mesylate group selectively to give 41. Catalytic hydrogenation then gave the corresponding ethyl 4-0-methylsulfonyl-2,3,6-trideoxy- -D-en/ /iro-hexoside in good overall yield (83%) (72). 

Currently, more group-selective and subtype selective compounds remain to be discovered. The recent demonstration of a possible action of new subtype selective... 

The reaction of tert-alkyl Grignard reagents with carboxylic acid chlorides in the presence of a copper catalyst provides ieri-alkyl ketones in substantially lower yields than those reported here.4,14 The simplicity and mildness of experimental conditions and isolation procedure, the diversity of substrate structural type, and the functional group selectivity of these mixed organocuprate reagents render them very useful for conversion of carboxylic acid chlorides to the corresponding secondary and tertiary alkyl ketones.15... 

Surfactants are prepared which contain carboxylic acid ester or amide chains and terminal acid groups selected from phosphoric acid, carboxymethyl, sulfuric acid, sulfonic acid, and phosphonic acid. These surfactants can be obtained by reaction of phosphoric acid or phosphorus pentoxide with polyhydroxystearic acid or polycaprolactone at 180-190°C under an inert gas. They are useful as polymerization catalysts and as dispersing agents for fuel, diesel, and paraffin oils [69]. 

E.R.H. Walker, The Functional Group Selectivity of Complex Hydride Reducing Agents, Soc. Reviews 5, 23 (1976). 

Compound Ref. Crystal Phase Space group Z Dihedral angle between the phenyl and cyclohexyl groups /° Selected intermolecular distances [A]... 

Hydrogenation of methyl salicylate gave mostly exs (25) implying that the last double bond to be reduced is often between the two functional groups. Selective esterification of diol (23) with p-bromobenzenesul-phonyIchloride (BsCl) gave (26) which cyclised in strong base. 

The result of enzymatic decarboxylation was extremely clear. While (S)-compound resulted in C-containing product, (/ )-compound gave the product with C no more than natural abundance. Apparently, the enzyme decarboxylated pro-(/ ) carboxyl group selectively and the reaction proceeds with net inversion of configuration. Thus, the presence of a planar intermediate can be reasonably postulated. Enantioface-differentiating protonation to the intermediate will give the optically active final product (Eig. 12). 

First of all it is necessary to determine the branching coefficient a, w hich is defined as the probability that a given functional group of a branch unit leads via a chain of bifunctional units to another branch unit. In a polymer of the type shown in Fig. 61, a is the probability that an A group selected at random from one of the trifunctional units is connected to a chain the far end of which connects to another trifunctional unit. As will be shown later, both the location of the gel point and the course of the subsequent conversion of sol to gel are directly related to a. 

The probability a that an unreacted A group selected at random leads... 

For more complete discussion of functional group selectivity of hydride reducing agents, see E. R. H. Walter, Chem. Soc. Rev., 5, 23 (1976). 

Indicate one or more satisfactory oxidants for effecting the following transformations. Each molecule poses issues of selectivity or the need to preserve a sensitive functional group. Select oxidants that can avoid the installation of protecting groups. In most cases, a one-pot reaction is possible, and in no case is a sequence of more than three steps required. Explain the reason for your choice of reagent(s). 

Tanaka, N., Goodeh, H., Karger, B.L. (1978). The role of organic modifiers on polar group selectivity in reversed-phase hquid chromatography. J. Chromatogr. 158, 233-248. 

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