M. Victoria Martín

Conjugate addition of diethylzinc to enones catalyzed by homogeneous and supported chiral Ni-complexes. Cooperative effect of the support on enantioselectivity

Abstract Chiral t-butylaminocarbonylpyrrolidine acetylacetonate Ni(II) hexafluorophosphate and the corresponding supported complexes on silica and on a modified USY-zeolite are readily prepared. The application of these free and supported complexes as catalysts in the addition of diethylzinc to a series of different substituted enones affords chiral β-ethylated ketones in high yields with an enantiomeric excess up to 95%.

Pseudoesters and derivatives. XXIII Reaction of 3-bromo-5-methoxyfuran-2(5H)-one with nucleophiles. Formation of cyclopropane derivatives

Abstract The reactions of 3-bromo-5-methoxyfuran-2 (5 H )-one ( 1 ) with nucleophiles in acetonitrile, in the presence of potassium carbonate and tetrabutylammonium bromide as a catalyst, are reported. The bromofuranone 1 reacts, with several carbon and oxygen nucleophiles to give the cyclopropane bis-lactones 7 , 8 , 11 or 12 . When 1 is reacted with diethylamine or propane-2-thiol in a 2:1 ratio, similar cyclopropane bis-lactones 16 or 21 , respectively, are formed. This behaviour is explained on the basis of a mechanism involving a double Michael addition, followed by ring closure via internal nucleophilic substitution of the halogen.

1,3-Dipolar cycloaddition of nitrile oxides to 2(5H)-furanones substituted at the 5-position by sulphur bearing groups

Abstract The behavior of the furanones 1–4 towards nitrile oxides 5–7 has been investigated, in particular with respect to the regio- and stereoselectivity. Cycloaddition of benzonitrile oxide (5) to 4,5-diethylsulphonylfuran-2(5H)-one (12) leads as sole addition product to the isoxazoline 30, that was easily aromatized to the isoxazole derivative 31, which is a useful synthon for the preparation of heteroanthracyclinone analogues.

Pseudoesters and derivatives. XXVI. Formation of cyclopropanes and five membered heterocycles by michael initiated ring closure reactions of 2-bromo-3-formylacrylic acid derivatives

Abstract The reaction of 3-bromo-5-methoxyfuran-2(5H)-onel with the stabilized carbanions derived from 2a–d, in a solid-liquid two-phase system in the presence of potassium carbonate and tetrabutylammonium bromide, affords the cyclopropane lactones 5a–d. With the ambident anions generated from 2e and 2f, the fused heterocyclic compounds 10 and 11, respectively, are obtained. The reaction of methyl 2-bromo-4,4-dimethoxy-2-butenoates (7, 8) with 2b–f, under similar conditions, gives rise to mixtures of the functionalized cyclopropanes 12b–f and 13b–f as mixtures of diastereoisomers; dihydrofurans 14 and 15 are also formed as minor components using ethyl acetoacetate (2f) as nucleophile.

Pseudoesters and Derivatives. XXXI1. Synthesis of 5-Ethylthio-, 5-Ethylsulfinyl- and 5-Ethylsulfonylfuran-2(5H)-ones

Abstract Convenient syntheses of 5-(ethylthio) furan-2(5H)-ones 2a-k from the appropriate 5-methoxyfuran-2(5H)-one 1a-g are described. The oxidation to the corresponding sulfoxides 5a-c and sulfones 6a-f is also reported.

6-Ethylsulfonyl-3-phenylfuro[3,4-d]isoxazole-4(6H)-one: A useful synthon for preparation of heteroanthracyclinone analogues

Abstract The synthon 6 was prepared from 4,5-diethylsulfonylfuran-2(5 H )-one (4) by 1,3-dipolar cycloaddition of benzonitrile oxide. Annelation of differently functionalized quinone monoketals with the anion of the isoxazole 6 affords a range of heteroanthracyclinone analogues.

Pseudoesters and derivatives. Part 37. 1,3-Dipolar cycloaddition of diazo compounds to 2(5H)-furanones substituted at the 5-position by sulfur bearing groups☆

Abstract The 1,3 dipolar cycloadditions of diazomethane and ethyl diazoacetate with differently substituted 5-sulfur-2(5 H )-furanones ( 1–6 ) are reported. Cycloaddition of diazomethane occurs in a regio- and stereospecific manner to give the expected adducts 9–14 , in good yield. The cycloaddition with ethyl diazoacetate occurs also in a regio- and stereospecific manner, but affords the corresponding 2-pyrazolines 15–19 .

Polycyclic Hydroxyquinones. Part 29. Regioselective Reactions of 5-sulphur-substituted furan-2(5H)-one anions with naphthoquinone monoketals. Application to the synthesis of anthracyclinone precursors

Abstract The anions of furanones 7 – 10 , reacted with naphthoquinone monoketals 11 – 15 to afford exclusively the C-5 substituted Michael adducts in good yield. The annelation reactions of the anions generated from furanones 30 and 33 with naphthoquinone monoketals 11 and 12 lead to 2-sulphur-substituted 1,4-anthraquinones 32 , 35 and 36 . Diels-Alder reaction of the 1,4-anthraquinones 41 and 42 with ( E )-1,3-bis[(trimethylsilyl)oxy]buta-1,3-diene ( 37 ) affords ABCD tetracyclic systems related to those existing in anthracyclinones. Furanones (a) react with monoketals (b) to afford Michael adducts (c) and/or the annelation products (d). The 1,4-anthraquinones are convenient synthons for the preparation of anthracyclinone precursors (e), via Diels-Alder reaction.

Synthesis of 2-sulphur-substituted 1,4-anthraquinones. Application to the synthesis of anthracyclinone precursors

Abstract 2-sulphur-substituted 1,4-anthraquinones 8a,b and 10 have been prepared by annelation reactions of the anions of furanones 5a,b with naphthoquinone monoketals of type 6 and 9 . Diels-Alder reaction of the 1,4-anthraquinones 11a,b with ( F )-1,3-bis(trimethylsilyloxy)buta-1,3-diene ( 12 ) affords ABCD tetracyclic systems related to those existing in anthracyclinones

Diels-Alder reactions with 2-methylpyridazin-3(2H)-ones bearing electron-withdrawing substituents at the 4- or 5-position

Abstract Diels-Alder reactions of 2-methylpyridazin-3(2 H )-ones, substituted with ethylsulphonyl, cyano and methoxycarbonyl groups at the 4- or 5-positions, with 1,3-dienes have been investigated. Pyridazinones behave as poor dienophiles and their reactivity depends on the nature and position of the substituents. 5-Substituted pyridazinones are more reactive than the 4-substituted isomers and high conversions to the expected adducts can be obtained after prolonged reaction times. Cycloadditions of ( E )-1-methoxybuta-1,3-diene proved to be regiospecific. The experimental results are largely in accordance with FMO calculations.