2 -Furanones, preparation

The procedure described is essentially that of Richet which has been repeated. The reaction is of interest since it provides a facile method of preparing tetrahydro-3-furanones which are useful reagents for alkylation in the Friedel-Crafts reaction. ... 

Owing to their frequent occurrence in natural products and their synthetic utility, 2(5//)-furanones are important synthetic targets and intermediates. In considering the methods for the preparation of these compounds, we will emphasize the recent developments in this area. 

Butynoate 29a reaeted with hexabutylditin in the presenee of PdCl2(PPh3)2 to give the 2,3-bis(tributylstannyl)aerylate 30a in nearly quantitative yield. But 30a eould not be eonverted to the 3,4-bis(tributylstannyl)-2(5//)-furanone 31. However, the analogous THP-proteeted bis(stannate) 30b prepared by a similar proee-dure reaeted with aeidie ion-exehange resin in methanolie solution the hydroxylie group of 30b was deproteeted and eyelization oeeurred to furnish the furanone 31 (Seheme 11) (99JOC328). 

An analogous reaction has been carried out using malononitrile and different products derived by a Cross-Aldol reaction of acetone (Scheme 32). The cyclic furanimide 91 was then reacted under microwave irradiation in the presence of NaOEt with a second molecule of malononitrile to give the furanone 92 [66]. The NLO chromophore 93 was prepared using this procedure. 

A rapid synthesis of carbon-14 labeled [l-14C]levulinic acid from simple building blocks has been demonstrated by Johansen and coworkers (Scheme 6.172) [324], In all three of the synthetic steps, starting from bromo[l-14C]acetic acid, microwave heating was used to accelerate the reactions, allowing a total preparation time of less than 1 h. The labeled levulinic acid was subsequently transformed into (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone in a bromination/oxidation sequence (not shown), a potent quorum sensing inhibitor. 

Trideoxy sugars have also been prepared from aldono- 1,4-lactones. Thus, 2-0-benzoyl-3,5,6-trideoxy-a-D,L-t/ira>hexofuranose was obtained (202) from L-rhamnono- 1,4-lactone via the furanone 155. L-Rhamnono-1,5-lac-... 

Although the preparative chemistry of (vinylketene)cobalt(I) complexes is relatively limited in the literature, the methods used include all the major procedures that have been more widely exploited in the analogous chromium and iron systems. There are many similarities between the intermediates involved in the synthesis of vinylketene complexes of iron, chromium, and cobalt, but as the metal is varied the complexes containing analogous ligands often exhibit significant differences in stability and reactivity (see Sections II and VI). Comparison of such species has often been an important aim of the research in this area. The (vinylketene)cobalt(I) complexes have also been shown to be synthetically useful precursors to a variety of naphthols, 2-furanones, ce-pyrones, phenols,6,22,95 >8, y-unsaturated esters,51 and furans.51,96a... 

The preparation of 2(5H)-furanone is the scaled-up and slightly modified procedure based on the report of Badovskaya that furfural is oxidized with perforraic acid to give a mixture of furanones. The preparation here is... 

The natural products as- and fra t-whisky lactones 95 have been prepared from the furanones 94 (92-93% yield), which were themselves obtained from ak-3-phenyl-6-butyl-3,6-dihydro-l,2-dioxin 92 and a chiral malonate ester 93 in 54% yield <20060L463> chromatographic separation on silica gel provided the pure (3R,43, 53)- and (33, 4i ,5R)-diastereomers of 94 which were converted into two nature-identical and two non-natural isomers of 95. 

With an ot, y-ketodiol, cyclization to produce a 3-furanone derivative is feasible, as is shown for the synthesis of ascofuranone (71) and geiparvarin (72) (Scheme 6.57) (286). The precursor for 71 was prepared by the cycloaddition of diene 66 to nitroalcohol 67. In this case, regioselective attack occurred only on the terminal double bond. Reductive cleavage-hydrolysis of the isoxazoline adduct 68 with Mo(CO)6 followed by acid-induced cyclization led to the furanone intermediate (286). A similar strategy was used for the synthesis of geiparvarin (72) (Scheme 6.58) (286). 

Chiral furanones (butanolides) such as 191 have been used as dipolarophUes in various 1,3-dipolar cycloadditions. The chiral 4-substituted butanolide 190 was prepared from 191 and the chiral auxiliary menthol (Scheme 12.55) (310,311). The single diastereomer 191 is obtained by crystallization and epimerization of the other diastereomer, as the amount of 191 in solution decreases. 1,3-Dipolar... 

Zask described a very clever and general approach to prepare 3-hydroxy-2(5H)-furanones in which he described the first report of a dianion of 179 that was utilized to prepare the key intermediate (Scheme 6.67, p. 116). After some experimentation he found that treatment of 179 with 2 equiv of ferf-butyllithium and 6 equiv of lithium chloride gave 319 that reacted cleanly with an ot-halo ketone to produce 320. Hydrolysis of 320 with refluxing 6 M hydrochloric acid then... 

In the second study, diketones were used as electrophiles and reacted with N-benzoylglycine to give a (Z/E) mixture of oxazolones 366 and 367 derived from condensation at the less hindered carbonyl group of the 1,2-dicarbonyl compound (Scheme 7.116). The ( )-isomers 367 were used as starting materials to prepare (Z) -5 - alky lidene- 3 - (benzoy lamino) -2(5//)-furanones 368... 

Preparation of 3-Substituted Dihydro-2(3f/)-furanones and 3-Substitutcd Tetrahydro-2A/-pyran-2-ones... 

Each desired enantiomer of 3-substituted dihydro-2(3.//)-furanones and 3-substituted tetrahydro-2//-pyran-2-ones was prepared starting either from 4,5-dihydro-2-(m-trimethylsilyloxy)oxazoles and alkylating with the corresponding alkyl halide, or by reversing the order of alkyl group introduction. Upon hydrolysis with dilute hydrochloric or sulfuric acid, 2-substituted cyclic lactones were obtained in 40-75% overall yield and 60-86% enantiomeric excess20. 

Hydroxy-2,5-dimethyl-3(2fT)-furanone is a widely used flavour molecule for fruit and brown flavours which is prepared by heating of rhamnose. A nitrogen-... 

Appropriately substituted diazo ketones have been converted into oxetanes in two instances by Wolf rearrangement processes. The structure of compound (52) was established by X-ray crystallography (69MI51300, 81CSC345). Reaction of 4,4-dibromo-2,2,5,5-tetramethyltetrahydro-3-furanone with aqueous base is a good method of preparation for 3-hydroxy-2,2,4,4-tetramethyloxetane-3-carboxylic acid (equation 90) (66JA1242). 

Furane derivatives were also prepared by the carbonylation of acetylene derivatives. Phenylacetylene was converted to the furanone derivative shown in 3.35. under reductive conditions, while in the presence of oxygen 2-phenylmaleic anhydride was isolated as the main product.43... 

Reaction of the 2-acetoxy-3(2//)-furanones (526) with monosubstituted hydrazines gives good yields of the pyridazinium-5-olates (527) together with varying amounts of isomeric products. Alkyl derivatives (527 R = alkyl) have also been prepared by base-catalyzed alkylation (Mel, Me2SO4, PhCH2Cl) of 3-methyl-6-phenyl-5-ethoxycarbonyl-4( 1 //)-pyridazinone. Reduction of the diphenyl compound 527 (R = Ar = Ph) by zinc and hydrochloric acid gives 3-ethoxycarbonyl-5-hydroxy-5-methyl-l,2-diphenyl-2-pyrrolin-4-one (528 R = Ar = Ph) (Scheme 21... 

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