3 -Furanon

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. ... 

Dodecyloxy-3-(2-chloroethyl)-2-methyl-4//-pyrido[l,2-n]pyrimidin-4-one 317 was obtained by cyclization of 3- l-[(3-dodecyloxy-2-pyridyl)ami-no]ethylidene -4,5-dihydro-2(3//)-furanone (316) in boiling POCI3 (95MIP4). 

Optically active dihydro-2-methylene-2(3//)-furanones fused to 5- and 6-membered carbocyclic rings were synthesized with 64-92% ee using the intramolecular reaction between chiral 2-alkoxy-carbonylallylsilanes and aldehydes80. 

S)-Dihydro-3-methylene-5-(2-methylpropyl)-2(3//)-furanone Typical Procedure9 ... 

Poorer diastereoselection occured in the case of the 3-substituted dihydro-2(3//)-furanones when lithium and copper(I) enolates were employed. 

Rapid reactions of linalool with OH radicals, NO3 radicals, and ozone in which the major products were acetone and 5-ethenyldihydro-5-methyl-2(3//)-furanone (Shu et al. 1997). 

These trivial names are permitted -y-butyrolactone, y-valerolactone, and S-valerolactone. Names based on heterocycles may be used for all lactones. Thus, -y-butyrolactone is also tetrahydro-2-furanone or dihydro-2(3//)-furanone. 

The photo [2 + 2] reaction between 5-methyl-2,3-dihydro-3-furanone (80) and methyl P-acetoxyacrylate (81) afforded a mixture of four adducts, from which the lactone (82) was isolated. The lactone (82) was reduced to the alcohol (53), which would rearrange quantitatively to the lactone aldehyde (84) upon treatment with... 

The photo-Fries rearrangement of aryl hydrogen (or methyl) succinates 267 leads to 4-(2-hydroxyaryl)-4-oxobutanoic acids (or methyl esters 268), which are readily cyclized to 5-(2-acetoxyaryl)-2(3//)-furanones (269) (Scheme 68). [189-191] Photolysis of 269 [191] or the analogous open-chain enol acetates [192,193] leads to chromones. 

Beckmann rearrangement of 2,2,5,5-tetramethyltetrahydro-3-furanone oxime (362) afforded 1,3-oxazine 363 in 64% yield (equation 158). 1,4-Oxazines 365 were obtained by acidic deprotection-spirocyclization of oxime ethers 364 (equation 159) . 

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). 

In smog chamber studies of the oxidation of 1-decene, octanal was the condensed-phase product formed in the next highest yield after nonanal, nonanoic acid, and dihydro-5-pentyl-2(3//)furanone (Forstner et al., 1997a). Write a plausible mechanism for its formation. 

The assignment of (/ )-2,3-dihydro-2-phenylfuran rests on Jones oxidation which furnished (ft)-dihydro-5-phenyl-2(3//)-furanone [(/ )-24]80. The configuration of the corresponding S-enantiomer (obtained by yeast reduction of 4-oxo-4-phenylbutanoic acid) was established by correlation with ethyl (S)-3-hydroxy-3-phenylpropanoate (of known configuration, obtained itself by a baker s yeast reduction) by a sequence featuring an Arndt -Eistert homologization as the key step (see also p 403)19. 

The conversion of (4S,5S)-dihydro-5-[(S)-l-hydroxyethyl]-4-trimethylsilyl-2(3//)-furanone (7, see p 416) into the (Z)-alkene 8 served to establish the relative configuration at C-4 and C-5 in 7 on the basis of the established double bond configuration in 8 and the anticipated (anti) stereochemistry of the elimination reaction (see also p474)81. 

R,5R)-5-[(lR)-l-benzyloxy-2-propenyl -dihydro-3-methyl-2(3H)-furanone 15 ( S,5R )-5- (/R )-t-benzyloxy-2-propenyf -dihydro-3-methyl-2(3 )-furanone... 

Either enantiomer of a-alkylated alkanoic acids, 3-substituted dihydro-2(3//)-furanones and 3-substituted tetrahydro-2//-pyran-2-ones with known absolute configuration and high optical purities can be obtained from metalation and alkylation of chiral 4,5-dihydrooxazoles (see Section 1.1.1.4.3.). 

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). 

Reactions of the Feist-Benary type have been applied to the synthesis of thiophenes (140 — 141) (75ZC100). The use of a-halocarbonyl halides provides an entree to 3-furanones (142 — 143) (73RTC73I). 

The term butenolide was first employed by Klobb for describing these compounds (1898BSF389). Chemical Abstracts currently has adopted the furanone system of nomenclature. Thus, A -butenolides are the 2(3//)-furanones and A ,/3-butenolides are the 2(5//)-furanones. The butenolide nomenclature still continues to be employed (76CRV625). 

In this review, we emphasize recent developments in the reactions of 2(3//)-furanones covering 10 years from 1987 until the end of 1996. 

Generally, 2(5//)-furanones (5) are thermodynamically more stable than their tautomers, the 2(3//)-furanones (4). SCF-MO calculations showed that the energy of 5a is less than that of its tautomeer 4a by 53 kJ/mol (70JA2929). 

He I photoelectron spectroscopic studies of the electronic structure of 2(3//)-furanone (4a) and 2(5//)-furanone (5a) were found to be consistent with their chemical stabilities. The IP (9.67 eV) of the HOMO of 2(3H)-furanone is significantly lower than the IP (10.65 eV) of the HOMO of the 2(5//)-furanone. Calculations for both molecules showed that the total energy of 5a is lower than that of 4a (94MI2). At room temperature, 2(3//)-furanone (4a), which is an unstable molecule, is formally converted into the 2(5//)-furanone (5a). This conversion involves a [1.3][Pg.277]

Furanones having an exocyclic double bond at position 3 follow a different course of isomerization. Thus, the furanones 13 and 14 isomerize in acidic medium to give the corresponding benzofuran and benzothio-phene carboxylic acids 15 and 16, respectively (Scheme 3) (90JPR414). 

Generally, acid or base hydrolysis of 2(3//)-furanones gives the corresponding y-keto acids. Refluxing furanones 17 and 19 with aq. sodium hy-... 

The behavior of 2(3//)-furanones is completely different from that of the isomeric 2(5//)-furanones (27), which on addition of benzonitrile oxide (28) give the furoisoxazolines 29,30, and 31 (Scheme 8) (96T3457). 

---