Chromanon

The isoflavone 406 is prepared by the indirect a-phenylation of a ketone by reaction of phenylmercury(II) chloride with the enol acetate 405, prepared from 4-chromanone[371]. A simple synthesis of pterocarpin (409) has been achieved based on the oxypalladation of the oriho-mercurated phenol derivative 408 with the cyclic alkene 407[372,373]. 

Chromanone, 3-acetamido-2-methyl-reduction, 3, 729 Chromanone, 3-amino-synthesis, 3, 734 Chromanone, 3-arylidene-thermoisomerization, 3, 722 Chromanone, 3-benzylidene-thermolysis, 3, 728 Chromanone, 3-bromo-2-hydroxy-benzofuran from, 3, 729 Chromanone, 6,8-dimethyl-hydroxymethylation, 3, 731 Chromanone, 2,3-epoxy-as synthon, 3, 735... 

Synthesis at 4-chromanones by condensation of saiicylaldehydes or o-hydroxyaryi ketones with enamines or ketones. 

R] (a) Hauser, C. R. Swamer, F. W. Adams, J. T. Org. React. 1954, 8, 59. [R] (b) Ellis, G. P., Chromenes, Chromanones, and Chromones from The Chemistry of Hetereocylic Compounds, Weissberger, A. and Taylor, E. C., eds John Wiley Sons, 1977, vol. 31, New York, p.495. Note The author in the former reference refers to the formation of chromones, coumarins, and flavones as the Kostanecki acylation while the latter author calls the formation of chromones and coumarins the Kostanecki-Robinson reaction. 

A comparison of the polarographic reduction of 2- and 3-substituted thiophenes have shown that the 2-isomers are more easily reduced than the 3-isomers. Polarography has also been used for the quantitative study of the dehalogenative reduction of 2-halo-5-carbonyl thiophenes and for the study of the hydroxychalcone-chromanone equilibrium in thienylsubstituted compounds. ... 

It is known that tropylium may be prepared from tropylidene via hydride abstraction by PhgC or MegC carbonium ions therefore, it is very likely that here too the dehydrogenation is a hydride transfer from the 1,5-dione to an acceptor. A similar dehydrogenation of chromanones to chromones, with triphenylmethyl perchlorate was reported. A study of the electrooxidation of 1,5-diones on a rotating platinum electrode showed that 1,5-diaryl-substituted diones afford pyrylium salts in these conditions and that the half-wave potentials correlate with yields in chemical dehydrogenations. 

Chlorobenzenes, sulphur-containing, reactivities of 590, 591 Chloropalladiosulphonylation 172 Chromanones, synthesis of 328 Chromatographic methods for detection and determination 111-113, 119-121... 

C22H32O3 15353-43-2) see Canthaxanthin (4-acetoxyretinyl)triphenylphosphonium chloride (04( 490102 15353-45-4) see Canthaxanthin 6-acetoxy-2,5,7,8-tctramethyl-2-(4-nitrophenoxymethyl>-4-chromanone... 

The mechanisms of the cyclisation of 2 -hydroxychalcone derivatives which can lead to flavanones, flavones and aurones have been reviewed <95MI1> and the formation of 3-hydroxy- chromanones and -flavanones from l-(2-hydroxyphenyl)-2-propen-l-ones via the epoxide has been optimised <96JOC5375>. 

The spin density of tocopheroxyl radical 2, a classical phenoxyl radical, is mainly concentrated at oxygen 0-6, which is the major position for coupling with other C-centered radicals, leading to chromanyl ethers 5. These products are found in the typical lipid peroxidation scenarios. Also at ortho- and para-positions of the aromatic ring, the spin density is increased. At these carbon atoms, coupling with other radicals, especially O-centered ones, proceeds. Mainly the para-position (C-8a) is involved (Fig. 6.3), leading to differently 8a-substituted chromanones 6. 

Kohar, I. Southwell-Keely, P. T. Reduction of 8a-hydroxy-2,2,5,7 8-pentamethyl-6-chromanone. Redox Report 2002, 7, 251-255. 

The 2,2-dialkylchromenes can easily be obtained from the reaction of coumarin 27 with a Grignard reagent.48 This method has been known for a long time and has not been modified much. The parent chromene 28 has been prepared by reduction and dehydration of 4-chromanone.63 Elimin-... 

A typical second step after the insertion of CO into aryl or alkenyl-Pd(II) compounds is the addition to alkenes [148]. However, allenes can also be used (as shown in the following examples) where a it-allyl-r 3-Pd-complex is formed as an intermediate which undergoes a nucleophilic substitution. Thus, Alper and coworkers [148], as well as Grigg and coworkers [149], described a Pd-catalyzed transformation of o-iodophenols and o-iodoanilines with allenes in the presence of CO. Reaction of 6/1-310 or 6/1-311 with 6/1-312 in the presence of Pd° under a CO atmosphere (1 atm) led to the chromanones 6/1-314 and quinolones 6/1-315, respectively, via the Jt-allyl-r 3-Pd-complex 6/1-313 (Scheme 6/1.82). The enones obtained can be transformed by a Michael addition with amines, followed by reduction to give y-amino alcohols. Quinolones and chromanones are of interest due to their pronounced biological activity as antibacterials [150], antifungals [151] and neurotrophic factors [152]. 

The orthometallation-carbonylation sequence illustrated in Scheme 155 affords a useful regiospecific methoxycarbonylation of the aryl ring of 4-chromanones.232 Unfortunately an extra step is incurred in the synthesis because of the unreactivity of the dimeric complexes (126) toward carbonyl insertion. 

Palladium-catalyzed cyclization reactions with aryl halides have been used to synthesize pyrazole derivatives. V-Aryl-lV-(c>-bromobenzyl)hydrazines 26 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2W-indazoles 27 . Palladium-catalyzed cascade intermolecular queuing-cyclocondensation reaction of o-iodophenol (28) with dimethylallene and aryl hydrazines provided pyrazolyl chromanones 29 <00TL7129>. A novel one-pot synthesis of 3,5-disubstituted-2-pyrazolines 32 has been achieved with an unexpected coupling-isomerization sequence of haloarene 30, propargyl alcohol 31, and methylhydrazine <00ACIE1253>. 

The methanochromanone 71 is converted with high trans-selectivity into the furo[2,3-fc]chromanone 72 by reaction with symmetric ketones (Scheme 50) <00H(53)657>. 

The following scheme shows that (2-propargyloxyphenyl)acyltellurides and (2-propar-gyloxyalkyl)aryltellurides undergo an intramolecular version of the above radical addition, promoted respectively by photolysis (tungsten lamp) and irradiation in the presence of (Bu3Sn)2 or BujSnH/AlBN giving chromanone and furan vinyltelluro derivatives (see also Section 5.7). 

---