3-methyl-4-chromanone

Typical procedure for rearrangement with aryl tellurium group transfer (formation of 3-[(aryltelluro)methyl]chromanones)f In a 5 mL flask fitted with a reflux condenser the telluroester (0.1 mmol) was photolysed under argon in benzene (3 mL) with a 250 W GE sunlamp from a distance of 15 cm. Either no cooling bath was used and the heat from the lamp caused the solution to reflux or the reaction was maintained at 8°C by means of a circulating cold water bath. After completion (TEC control) the solvent was removed in vacuo and the residue analysed by NMR spectroscopy. 

In every case the product mixture was composed of the expected 2-((aryltelluro) methyl)chromanone as the very major product together with the corresponding elimination product and the diaryl ditelluride. Spectral analysis was facilitated by the possession of authentic samples of the ditellurides and, eventually, of the elimination products. The product ratios, and hence yields, were determined by integration of the NMR spectra. Attempted purification by chromatography on silica gel led only to less pure samples contaminated with increased amounts of ditelluride and elimination products. 

This year has seen the publication of the first convenient synthesis of crotonophenones, which are open chain forms of benzopyranones (chromanones). Previous attempts at their synthesis via Friedel-Crafts or simple aldol reactions gave poor yields. However, it has now been shown that the dianion of n-hydroxyacetophenones will react with aldehydes, and dehydration of the products constitutes a simple synthesis of crotonophenones and also of 2-methyl chromanones. 

Hydroxy-(X,X0-dimethoxy-2-methyl- chromanone Arachniodes standishii Ohwi C12H14O5 83-86 29... 

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... 

In principle, the relative configuration in these and related cases can be identified by spectroscopic analysis, however, in practice this is not always simple to achieve. For example, the conjugate addition of a methyl group to the racemic chromone rac-9 could generate four pairs of diastereomeric chromanones (rac-10-rac-13). In the event, two main products in a 4 1 ratio were obtained. The relative configuration was not clear from the H-NMR coupling constants (J2,3) and was, therefore, determined by chemical reactions108 (see pp 472 and 480). 

In addition to the two types of products formed by osmium tetroxide in Scheme 9 is its action on 5,10-diacetoxy-2-methyl-2//-naphtho[2,3-6]pyran (172) in conjunction with sodium chlorate at room temperature to give a mixture of stereoisomeric chromanones (173) (78CB1285). 

Tetrahydropyran-4-ones, for example diethyl 6-methyl-4-oxotetrahydropyran-3,3-dicar-boxylate (600), are brominated at C-3 (77JCS(Pl)l647). Chromanones are readily halogenated at C-3 (see above) when they are treated with phosphorus pentachloride, the reaction does not stop at monochlorination the carbonyl group is attacked and 3,4-dichloro-2//-chromene (601) is formed, an uncommon conversion of a chromanone into a chromene (79TL3901). Chroman yields 4- and 6-bromides when treated with NBS-benzoyl peroxide. 

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). 

Chromanone, 7-methoxy-2,2-dimethyl-reactions with alkali, 3, 728 Chromanone, 3-methyl-reduction, 3, 730... 

In an attempt to use phenolic Mannich bases in a synthesis of 3-chromanones, a mixture of 1 -[(dimethylamino)methyl]-2-naphthol and a-chloroacrylonitrile was heated under reflux in anhydrous dioxane. The product, however, which was formed in 55% yield, was shown to be the naphthonaphthopyranopyran 1. 

The fixed geometry of a, 3-unsaturated ketones in the S-cis form, as observed in arylidene alkanones, influences their reactivity. For example, the reaction of arylhydrazines with 3,5-diarylidene-4-piperidones, 2-arylidene-l-tetralones, 2,6-diarylidenecyclohexanones and 2-arylideneindan-l,3-diones requires stronger conditions than for the case of their noncyclic analogues [76, 77, 78, 79, 80, 81, 82, 83, 84]. However, arylidene derivatives of cyclohexanone, 1-indanone, 4-chromanone, 4-thiochromanone and TV-methyl-4-piperidone hydrochloride react with hydrazines more easily [85,86,87,88], It is interesting to note that the more complicated and sterically hindered unsaturated ketones of the spiro type 64 react with hydrazine and phenylhydrazine very easily in the presence of piperidine, leading to pyrazoles 65 in high yields [89] (Scheme 2.16). 

Flavanones undergo a variety of transformations by HTI or other hypervalent iodine reagents. In methanol, at room temperature, they were dehydrogenated to the corresponding flavones [40], A similar dehydrogenation occurred in chromanones [41]. Dramatic solvent effects occurred when methanol was replaced by other solvents. Thus, in trimethyl orthoformate ring-contraction was the main pathway and methyl 2-aryl-2,3-dihydrobenzofuran-3-carboxylates the major products, accompanied by substantial amounts of 3-methoxyflavones [42] ... 

Monoacyl-type protecting groups are not recommendable for N -protection, since racemi-zation of the related amino acid derivatives during carboxy activation for their coupling represents a serious problem. Consequently, Ai-acyl derivatives such as formyl or tri-fluoroacetyl have been used mainly for side-chain protection. Nevertheless, some new N -derivatives, which address this problem, have been proposed. With the quinone-derived acyl-type protecting group 3-methyl-3-(2,4,4-trimethyl-3,6-dioxocyclohexa-l,4-dienyl)butyryl (74) (Scheme 39) racemization is almost totally suppressed, and it is readily cleaved with sodium dithionite with formation of the chromanone byproduct The Al -(alkyldisulfa-... 

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