2-Phenyl-chromanones

Flavonoids are more or less intensely yellow colored pigments belonging either to the group of 2-phenyl-chromones 39 (flavones, flavonols) or 2-phenyl-chromanones 391 (flavanones, flavanonols) both groups have a backbone of 2-phenyl-l,4-benzopyrones ... 

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]. 

Another problem for the synthetic use of PFR is that the ortho-rearranged products may act as internal light filters, stopping the reaction. In synthetic routes leading to chromanones, chromones, and related compounds, this is of vital importance because the overall yield is limited by the photochemical step. Improved yields can be obtained if the a, 3-unsamrated orr/io-hydroxyphenones resulting from PFR are removed and cyclized to chromanones. This can be acomplished in one pot by irradiation in a two-phase system benzene/10% aqueous NaOH, whereby chromanones are directly obtained from phenyl crotonates in 80-90% yields [210]. 

Hydroxyacetophenone and related compounds are attractive precursors of chromanones, most notably in the synthesis of their 2-phenyl derivatives. Being adjacent to the carbonyl group, the methyl group of the acetophenone is activated and forms a carbanion on treatment with base. Subsequent condensation with a carbonyl compound which lacks an a-hydrogen atom leads to a 1,3-dicarbonyl or an enone system which readily cyclizes to a chromanone. Thus, methyl formate affords the chromanone (591) (53MI22400) and formaldehyde has been used in the synthesis of 3-methylchroman-4-one from o-hydroxypropiophenone (68T949). 

The (—)-quinine-catalyzed IMA of 40 gave cw-(- -)-methoxy chromanone cou-marin (cA-41) in 67% yield with 98% ee and its trans-41 in 21% yield with lower eantioselectivity (39% ee). The Mgl2-assisted isomerization of cis-(+)-41 accompanied by demethylation followed by the reaction of the formed diastereomeric mixture of chromanone 42 (without separation) with senecioyl aldehyde in the presence of phenyl boronic acid under the same condition to construct the 2,2-dimethyl chromanone ring reported in the synthesis of (+)-inophyllum B (3). The yield of trans-(+)-43 in 61% with 91% ee and its cw-isomer (+)-43 corresponded to the (+)-calanolide D as a minor product in 23% yield with 84% ee. At last, the synthesis of (+)-calanolide A (1) was accomplished by hydride reduction of (+)-43 with... 

The kinetically controlled Meerwein - Ponndorf-Verley reduction of 2-phenyl-4-chromanone (llavone, 3) affords c -2-phenylchroman-4-ol [ax-4-flavanol, 4 (85%)]19 i 2n. 

C-1,4-Phenyl migration. A soln. of 1 g. l,l,5,5-tetraphenyl-3,3-dimethyl-l-pentene in re/ r-butanol irradiated 10 hrs. with the Corex glass-filtered light of a 450 w. Hanovia medium-pressure lamp under deoxygenated Ng -> 150 mg. 1,4,5,5-tetraphenyl-3,3-dimethyl-l-pentene (and 760 mg. recovered startg. m.). H. E. Zimmerman and R. D. Little, Am. Soc. 96, 5143 (1974) C-phenyl migration in 3-chromanones s. A. Padwa and A. Au, Chem. Commun. 1975, 58. 

The precursors of flavonoid biosynthesis include shikimic acid, phenylalanine, cinnamic acid, and p-coumaric acid. Shikimic acid acts as an intermediate in the biosynthesis of aromatic acid. The basic pathways to the core isoflavonoid skeletons have been established both enzymatically and genetically [16]. The synthesis of isoflavones can be broadly divided into three main synthetic pathways the formylation of deoxybenzoins, the oxidative rearrangement of chalcones and flavanones, and the arylation of a preformed chromanone ring. In leguminous plants, the major isoflavonoids are produced via two branches of the isoflavonoid biosynthetic pathway, and the different branches share a majority of common reactions [1]. Unlike the common flavonoid compotmds, which have a 2-phenyl-benzopyrone core structure, isoflavones, such as daidzein and genistein, are 3-phenyl-benzopyrone compounds. Biochemically, the synthesis of isoflavones is an offshoot of the flavonoids biosynthesis pathway. Several attempts have aimed to increase... 

Hydrolysis methods for mono[ C]nitriles and the spectrum of chemical transformations of the resulting [l- C]carboxylic acids differ little from those for their unlabeled counterparts, so that the synthesis of [l- C]tetralones 42 and [l- " C]indanones 46 from w-arylalkyl [ C]nitriles will suffice as examples (Figure 7.11). Acid-catalyzed hydrolysis of 4-phenylbutyro[ C]nitrile followed by polyphosphoric acid-mediated cyclization of the resulting phenyl[l- C]butanoic acid converted it into 42 in 89% radiochemical yield. Sequential bromination and oxime formation provided the a-bromooxime 43, which upon treatment with polyphosphoric acid underwent a Beckman rearrangement to provide the ring-expanded tetrahydro-2H-l-[2- C]benzazepine-2-one derivative 44- This was a key intermediate for the preparation of a series of labeled ACE inhibitors" . The acid-catalyzed cyclization of a mixture of 3-(2-hydroxyphenyl[l- " C]propionic acid and its ethyl ester, prepared by treatment of the propio[ " C]nitrile with ethanolic HCI proved to be a two-step sequence. In the first step, 2- [2- " C ]chromanone I4SI was formed and had to be submitted to... 

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