Phloroglucinols, selectivity

A unique feature of this procedure is the selective monode-methylation of the dimethyl ether. The scope of this reaction is illustrated6 in part by the preparation in high yield of p-methoxyphenol, guaiacol, and phloroglucinol dimethyl ether from the respective fully O-methylated compounds. An exception is pyrogallol trimethyl ether which affords pyrogallol 1-monomethyl ether in high yield.6... 

Protonated phenols and phenol ethers formed in superacids can be trapped by aromatics (benzene, naphthalene, tetrahydroquinoline). The products are either cyclohexenone derivatives301 [Eq. (5.112)] or aryl-substituted phenols. In the reaction of phloroglucinol with benzene, the diphenyl-substituted derivative is the main product [Eq. (5.113)], whereas 1,3,5-trimethoxybenzene gives selectively the monophenyl derivative (80% yield). Protonated dicationic species, such as 76, detected by Olah and Mo302 using NMR, were suggested to be intermediates in these processes. 

Generally, there is substantial selectivity in these condensation reactions for the p-hydroxybenzyl alcohol. Earlier work (5,6) had shown that the o-isomer reacted preferentially at the C-8 of (+)-catechin, whereas, there was little regios-electivity in reactions with the p-isomer. One might suspect that phloroglucinol and (-l-)-catechin would preferentially react with the p-isomer because of less steric hindrance. The results support that, but they also show that resorcinol exhibits this same preference for reaction with the p-isomer. Because of the dominance of the p-isomer in these reactions, there is little regioselectivity in... 

The initial synthetic entry into the aflatoxin system was communicated by Buchi66,136 and reported the total synthesis of aflatoxin Bj (1). The key elements of construction for this effort were, the selective differentiation of the phloroglucinol nucleus, and the formation of the functional precursor of the ABC system in the guise of the 4-methylcoumarin (49). Upon scrutinization of this molecule, it becomes evident that all of the requisite carbon atoms (see numbers) for the constitution of the ABC ring system are indeed present, albeit not necessarily in the proper level of oxidation. This fundamental coumarin piece (49), was arrived at by the implementation of two basic strategies. 

It was found that carbazole and phloroglucinol are unsuitable for determining the heptose content of sugar mixtures because of interference from other sugars similar interference is encountered with resorcinol. With orcinol, cysteine, and diphenylamine, however, specific reactions can be obtained at selected wavelengths. Ketoheptoses (and keto sugars in general) react under milder acid conditions than the aldoses, and this property can be used for identification purposes. In the orcinol test, for... 

Recent teports from our research groups have demonstrated that neat supercritical CO2 is selective for the extraction of hyperforin and adhyperforin in St. John s wort (24, 33) (Figure 2). Modifiers do not increase toe SFE recoveries of these phloroglucinols, but tend to cause partial extraction of polar compounds in St. John s wort. Thus, extraction with neat CO2 is toe best choice for selective removal of hyperforin and adhyperforin from St. John s wort. 

A similar approach can also be applied to create a nanoporous network having two different polymerizable units. Lee published an LC formed by H-bonds between phloroglucinol and pyridine derivatives [69]. These molecules were mixed in a 1 3 ratio to form a star-shaped discotic columnar phase. The pyridine derivative contains two different photoreactive polymerizable groups in the alkyl chain. These groups, diacetylene and acrylate, might be selectively polymerized along the vertical and horizontal axes. The core molecules are removed with a sodium hydroxide treatment, to create the nanoporous conjugated network. These pores have a pyridine interior and an estimate pore size of 1 mn. 

The Pechmann condensation served as a key ring-forming reaction in Xu and co-workers s synthesis of the HIV-1-selective nonnucleoside reverse transcriptase inhibitor calanolide A (39). In this work, phloroglucinol (35) and ethyl butyrylacetate (36) were condensed in sulfuric acid at 90 °C to provide 5,7-dihydroxy-4-propylcoumarin (37) in nearly quantitative yield on 150 g scale. Subsequent Friedel-Crafls acylation of 37 followed by condensation of the acylcoumarin product with 4,4-dimethoxy-2-methylbutan-2-ol provided pyranylcoumarin 38, which was converted to... 

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