Chromans, 3-acyl

Chroman, 4-(p-hydroxyphenyl)-2,2,4-trimethyl-X-ray studies, 3, 622 Chroman, 2-methoxy-synthesis, 3, 806 Chroman, 5-methoxy-synthesis, 3, 778 Chroman, 7-methoxy-synthesis, 3, 778 Chroman, 8-methoxy-acylation, 3, 732 Chroman, 2-methoxy-2-methyl-synthesis, 3, 780 Chroman, 2-methyl-synthesis, 3, 785 Chroman, 5-methyl-reactivity, 3, 732 Chroman, 6-nitro-synthesis, 3, 784 Chroman, 4-phenyl-synthesis, 3, 783 Chroman, thio-metabolism, 1, 241 Chroman, 5,6-thio-2-substituted... 

Propionic acid, 2-bromo-3-(3-indolyl)-methyl ester rearrangement, 4, 279 Propionic acid, 3-(3,4-dimethyoxyphenyl)-dihydrocoumarin synthesis from, 3, 848 Propionic acid, indolyl-synthesis, 4, 232 Propionic acid, 3-(l-indolyl)-sodium salt pyrolysis, 4, 202 Propionic acid, 3-(3-indolyl)-intramolecular acylation, 4, 220, 221 Propionic acid, 3-phenoxy-chroman-4-one synthesis from, 3, 855 Propionic acid, 3-(3-phenylisoxazoI-5-yl)-bromination, 6, 25... 

In the above cases, the photoreactivity of indole, coumarin, pyridine, and so forth, does not compete effectively with PFR, which becomes the major reaction. However, in the case of the chromene depicted in Scheme 28, the electrocyclic ring opening prevails over PFR. By contrast, the analogous chromane undergoes clearly acyl migration [86]. 

Bromination, chlorination, nitration and Friedel-Crafts acylation of chroman give the 6-substituted derivatives in good yields by standard methods. When 6,8-dimethyl-chromanone (677) is warmed with formaldehyde in sulfuric acid, hydroxymethylation at C-5 occurs (78BCJ1874). 

The chroman ring system is stable to organometallic reagents, for example in the formation of the tertiary alcohol (690) in high yield (63HCA650), and to the usual interconversion of carboxylic acid, acyl chloride, carboxamide and nitrile. 

A facile peri-ring closure of dimethylnaphthol ether 1075 proceeds via ester hydrolysis and conversion to the corresponding acid halide followed by an intramolecular Friedel-Crafts acylation to afford the tricyclic chroman-3-one 1076, an intermediate during a formal synthesis of mansonone F (Equation 421) <2000CC1203>. 

Acyl radical 1095 generated from the hydrazide 1094 can undergo cyclization and reaction with diphenyldiselenide to afford the chroman-4-one 1096 in good yield (Scheme 273) <2003CC204>. 

Exposure of the diazonium salt 1107 to iodide ion generates an aryl radical, which undergoes intramolecular homolytic substitution at sulfur to liberate the acyl radical intermediate 1108. An exo-mode cyclization with concomitant incorporation of iodide then occurs to afford the 3-disubstituted-chroman-4-one 1109 in excellent yield (Scheme 275) <1997JOC5982>. 

There has been a number of developments in the use of salicylaldehydes as precursors of both chromenes and chromans. Alkenes activated by acyl, formyl, nitrile and phenylsulfonyl groups react with 2-hydroxybenzaldehydes and 2-hydroxy-1-naphthaldehyde under Bayliss-Hillman conditions to yield 3-substituted chromenes via the in situ dehydration of the initially formed chroman-4-ol <02JCS(P1)1318>. In like manner, P-nitrostyrenes yield 2- and 2,2-substituted derivatives of 3-nitrochromenes <02H(57)1033>. A simple route to 2-phenyl-2H-chromenes starting from salicylaldehyde and utilising a Pd(0)-catalysed cyclisation of an allylic acetate has been described <02SC3667>. 

The outcome of the reaction of phenols with 5-alkylidene Meldrum s acids 25 catalysed by Yb triflate in the synthesis of O-heterocycles is dependent upon the nature of the alkylidene unit. Two distinct Friedel-Crafts sequences are apparent in this mild and simple route to coumarins and dihydrocoumarins and to chromones and chroman-4-ones (i) C-alkylation - (9-acylation and (ii) C-acylation - (9-alkylation <06JOC409>. 

Chroman 2-[4-(bzw. 5)-Nitro-2-pyrryl]-4-oxo- VI/4, 154f. Hydroxvlamin, N-Benzoyl-N-(3-nitro-phenyl)- E16a, 61 (N02-Red./N-Acyl.)... 

SoHman et al. reported the synthesis of 3-triphenylphosphoranylidene-chromanes 117 from Mannich bases 115 of the commercial moUusddde niclosamide and the ciunulated yhdes 2, 82 or 88 [73]. The reaction was carried out in boihng toluene and is thought to proceed by initial addition to give the acyl ylides 116, which then cycHze by the unusual expulsion of a secondary amine, i.e. by nudeophihc attack of the ylidic carbon atom at the benzyhc carbon atom. Intermediates 116 were not isolated. The moUusdddal activities of compounds 117 were found to be about tenfold lower than that of the parent niclosamide (Scheme 25). 

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