Showing papers on "Pyran published in 1979"

Polyketo-enols and chelates. Chemistry of the formation of xanthophanic enol and its glutaconate and pyran intermediates

Abstract: The formation mechanism for xanthophanic enol (3) under ‘melt’ conditions is clarified by stepwise synthesis via 2,4-diacetylglutaconic ester (1) and the anion from methyl 5-acetyl-6-oxo-2-methyl-6H-pyran-3-carboxylate (11).Dimethyl 2,4-diacetylglutaconate exists mainly as the cyclic form (4) in solution, and increasing in solvent polarity, increasing temperature, or catalysis by pyridine, promotes n.m.r. equivalence of the acetyl methyls. In the case of 1,1,3,3-tetra-acetylpropene, first two, and then all four acetyl methyl signals coalesce showing an equilibrating system of cyclic structures involving hemi-acetal and Z–E changes. 1,1,3,3-Tetrakismethoxycarbonylpropene has a normal acyclic structure (9).Glutaconate (1) gives methyl 5-acetyl-6-oxo-2-methyl-6H-pyran-3-carboxylate (11) when treated with sodium methoxide (0.5–4.0 mol) : at higher concentrations (12 mol) the aldol product dimethyl 5-hydroxytoluene-2,4-dicarboxylate (15) and its half-ester are formed. With magnesium methoxide as base, 1 mol or less gives the pyran (11), but the compounds with 2 mol and above are the Claisen product methyl 5-acetyl-2,4-dihydroxybenzoate (18) and the aldol product (15). These differing responses to bases are considered, and the effects of magnesium chelation on reactivity are discussed in terms which explain why Claisen condensations are favoured whilst aldol condensations are disfavoured during anion attack on the chelate.

Spiro-polycyclicimidazolidinedione derivatives

Abstract: Novel spiro-polycyclicimidazolidinedione derivatives useful as aldose reductase inhibitors and as therapeutic agents for the treatment of chronic diabetic complications are disclosed. The derivatives include 2',3'-dihydro-spiro[imidazolidine-4,4'-[4'H]-naphtho[1,2-b]pyran]-2,5-dione, 2',3'-dihydro-spiro-[imidazolidine-4, 4'-[4'H]-naphtho[1,2-b]thiopyran]-2,5-dione, 1',2',3',4'-tetrahydro-spiro[imidazolidine-4,1'-benz[a]anthracene]2,5-dione, 2',3'-dihydro-spiro[imidazolidine-4,1'phenalene]-2,5-dione, 1',2',3',4'-tetrahydro-spiro[imidazolidine-4,1'-phenanthrene]-2,5-dione, the 2,1 isomers of the 2',3'-dihydro-4'H-pyran and 2',3'-dihydro-4'H-thiopyran derivatives, the 2',3'-dihydro-4'H-anthracenopyran and 2',3'-dihydro-4'H-anthracenothiopyran derivatives, the spiro-4,4' isomer of the tetrahydrophenanthrene derivative, the [b] isomer of the benzanthracene derivative and the mono or disubstituted 2',3'-dihydro-4'H-naphthopyran, 2',3'-dihydro-4'H-naphthothiopyran and tetrahydrophenanthrene derivatives.

Derivatives of 2H-pyran-2-one

Abstract: Processes for producing a (1α, 4α, 5α)-6,6-dimethyl-4-halo-substituted-methyl-3-oxabicyclo[3.1.0]hexan-2-one and its novel intermediates from known and inexpensive starting materials are described and exemplified.

The molecular rearrangements of cyclopropyl epoxides generated from various flavonoid systems

Abstract: The fused three-ring systems, naphtho[1,2-c]pyran and 1H-pyrano[4,3-b]benzofuran, were obtained by the reaction of αβ-unsaturated ketones and cyclopropyl ketones with DMOSM and DMSM, presumably via cyclopropyl epoxides. An attempt to prepare a pyranobenzopyran by reaction of a 3-bromo-2,3-dihydrochromenone with DMOSM gave 1a,7a-dihydro-1a-phenylcyclopropa[b]chromen-7(1H)-one and a ring-contracted product, a spiro[benzofuran-2,1′-cyclopropan]-3(2H)-one; methylenation of both products gave benzofurans. The αβ-unsaturated carbonyl group of 2-phenylchromen-4-one reacted with DMOSM to give, as well as 1a,7a-dihydro-1a-phenylcyclopropa[b]-chromen-7(1H)-one, diastereoisomeric 2-(methylphenylmethylene)benzofuran-3(2H)-ones, a thiin oxide, and a 2,3-dihydro-3-methylenebenzofuran.

Synthesis and properties of spiropyrans that are capable of reversible opening of the pyran ring (review)

Abstract: The review is devoted to spiropyrans in which the pyran ring can be opened reversibly to give a completely conjugated colored isomer. Methods for the preparation of spiropyrans from various heterocyclic systems, their chemical properties, and the effects of various factors on the relative stabilities of the spiropyrans and the isomeric merocyanines are examined.

Photosubstitution of 1,2,4,5-tetracyanobenzene by ethers

Abstract: Irradiation of a mixture of 1,2,4,5-tetracyanobenzene and diethyl ether, tetrahydrofuran, or tetrahydropyran gave the corresponding substitution product, 1-ethoxy-1-(2,4.5-tricyanophenyl)ethane, tetrahydro-2-(2,4,5-tricyanophenyl)furan, or tetrahydro-2-(2,4,5-tricyanophenyl)pyran. Three possible mechanisms involving electron transfer are discussed.

Synthesis and reaction of 3-hydroxytetrahydro-4H-pyran-4-one

Abstract: Photosensitized oxygenation of 5,6-dihydro-4-methyl-2H-pyran (1) in methanol followed by reduction gave two kinds of allyl alcohols [(2) and (3)] together with the epoxy-ethers (4) and (5). When the reaction was carried out in solvents other than alcohols it gave (2) and (3) exclusively. Ozonization of 4-methylenepyrans (2) and (13) followed by reduction with zinc powder–acetic acid afforded 3-hydroxytetrahydropyrans (11) and (14). Bromination of (14) gave the dibromide (16), which yielded bromopyran (17) and 3-acetoxy-4H-pyran-4-one (18) on treatment with 1,8-diazabicyclo[5.4.0]undecene. However, the reaction of (16) with silver acetate in acetic acid predominantly afforded (17) in excellent yield. Other allied reactions and mechanisms of these reactions are described.

Derivatives of fused 3-hydroxymethyl-pyran-4-ones as a mobile keto–allyl system

Abstract: Syntheses of 3-hydroxymethyl-4H,5H-pyrano(3,4-c)(1)benzopyran-4-one, 7, and 3-hydroxy-methyl-4H,5H-(1)benzothiopyrano(4,3-b)pyran-4-one, 8, from 2,2-difluoro-4-methyl-5H-(1)benzopyrano- and (1)benz...

Polyketo-enols and chelates. Product control by magnesium chelation in the rearrangement of dimethyl xanthophanic enol and other xanthyrones

Abstract: The products formed when dimethyl xanthophanic enol (1) is treated with magnesium methoxide depend strikingly on the molar ratio of the reactants. Up to near a 1 : 1 molar ratio of methoxide to enol, the enol is recovered unchanged. At a 1 : 1 molar ratio the main product is the isophthalate (11) formed by aldol reaction. When the molar ratio is >2 : 1, the main product is the pyran (13) and formation of (11) is much diminished. At a 3 : 1 molar ratio no isophthalate (11) is formed, pyran (13) has diminished in amount, and the resorcylic ester (14), a product of Claisen condensation, is now dominant. At a >6 : 1 molar ratio of magnesium methoxide to enol the resorcylic ester is the sole product, formed in high yield. These results are explained in terms of methoxide-initiated pyran opening and the role of the resulting mono- and bis-magnesium chelated species as substrates for aldol and Claisen rearrangements. The protective action of magnesium complexing on an otherwise base-sensitive chain is also a significant factor. For comparison, the reaction of dimethyl xanthophanic enol is examined using initial sodium methoxide : enol ratios of 1–24 : 1. Only the aldol product, the isophthalate (6, R = H), is formed across the whole concentration range.The ester-interchange situation, when variously substituted xanthyrones are transformed into resorcylic esters by excess of magnesium methoxide, is studied in support of the proposed mechanisms. The xanthyrones (34)–(36), without a pyrone acetyl and thus incapable of undergoing the resorcylic ester transformation, form substituted pyrans (39)–(41). Sodium methoxide, however, causes chain degradation and cyclisation of the major fragment to dimethyl 4-hydroxyisophthalate, again demonstrating a substantial diversion of reaction pathway resulting from the complexing effect of magnesium methoxide.

Psychopharmacological study with K 8409, a 1H-naphtho[2,1-b]pyran 3-dialkylamino substituted derivative.

Abstract: A 1H-naphtho[2,1-b]pyran derivative (K 8409) has undergone pharmacological investigation for psychotropic activity. The results show potential antidepressant action quantitatively similar to that of imipramine and amitriptyline, but due rather to MAO inhibition than to imipramine-like activity; interestingly enough, anti-MAO activity was particularly selective for the serotonin-converting enzyme, both centrally and peripherally. The outcome of the other tests suggests that the incidence of untoward effects is likely to be limited.

Synthesis of Polyenamines with Pendant Hydroxyl Groups by Ring-Opening Polyaddition of 5,5′-Oxalylbis(3,4-dihydro-2H-pyran) with Diamines

Abstract: A new class of polyenamines with pendant hydroxyl groups was synthesized by the ring-opening polyaddition of 5,5′-oxalylbisi(3,4-dihydro-2H-pyran) with diamines through vinyl-ogous nucleophilic substitution. Solution polymerization carried out in alcoholic solvents such as m-cresol at room temperature afforded polymers having inherent viscosities of 0.1–0.27 in quantitative yields. The hydroxyl-containing polyenamines were soluble in a limited number of solvents and had low softening temperatures, below 200°C.

pseudo-Azulenes. Part 7. Crystal and molecular structure of benzo-[b]indeno[1,2-e]pyran

Abstract: X-Ray diffraction of the title compound shows that the molecule is planar. The bond lengths of the central cyclopenta[b]pyran system indicate pronounced bond alternation and hence little aromatic character. The results of ωβ-calculations are in good agreement with the experimental bond distances.

Norbornyl-substituted pyran perfumes

Abstract: Norbornyl-substituted pyrans, their preparation and their use as olfactory components of perfume formulations are disclosed.

Pyran analogs of 5-hydroxy-PGI1

Abstract: The present invention provides pyran analogs of 5-hydroxy-PGI1, which are useful pharmacological agents. These analogs of prostaglandin I1 are useful for the stimulation of mammalian smooth muscle tissues.

A direct PMR study of dienone-2h-pyran valence isomerization in 1,1-dicarbonyl 1,3-dienes

Abstract: 1. Direct measurements have, for the first time, been carried on dienone-2H-pyran isomerization in 1,1-dicarbonyl 1,3-dienes. 2. A study has been made of the effect of solvent and substituents on the position of the point of equilibrium in such systems; thermodynamic and activation parameters have been determined for the isomerization process, and the effect of the solvent on these parameters have been studied. 3. Reducing the efficiency of conjugation and increasing the steric strain in the dienone shifts the points of dienone-2H-pyran equilibrium to the pyran side. An increase in the dipole moment of the solvent has the opposite effect. 4. The solvent has little effect on rate constant values for the dienone-2H-pyran isomerization.

Synthesis and X-ray structure of a cyclopenta[d]furo[2,3-b]furan derivative from isomerisation of 3,4,4-triacetyl-2-methyl-cis-4,4a,5,7a-tetrahydrocyclopenta[b]pyran

Abstract: 3,4,4-Triacetyl-2-methyl-cis-4,4a,5,7a-tetrahydrocyclopenta[b]pyran (3), obtained by reaction of tetra-acetyl-ethylene (1) with cyclopentadiene, was converted into a mixture of the trans-isomer (4) and 3,3a-diacetyl-2,7a-dimethyl-3aα,4,6aα,7aα-tetrahydro-3bαH-cyclopenta[d]furo[2,3-b]furan (5), a new heterocyclic system, whose structure was definitively established by an X-ray analysis. Crystals are orthorhombic, a= 15.824(5), b= 15.465(5), c= 11.129(4)A, Z= 8, space group Pbca. The structure was solved by direct methods and refined by least squares to a final R of 0.073 for 1 665 observed reflections. Some aspects of the mechanism are discussed.