P. de March

Spectroscopic properties and photochemical behaviour of polymers with covalently bound tris(bipyridine)ruthenium(II) complex. Use of a hydrophilic chain as spacer

Abstract The synthesis of a tris(bipyridine)ruthenium(II) complex, covalently bound through a polyethoxylated chain to an insoluble polymer is described. The spectroscopic properties of several Ru(bpy)32+ complexes anchored to insoluble polystyrene supports, and of the monomeric complex are compared and shown to be very similar. Methyl viologen luminescence quenching studies of the excited state of the polymer show behaviour different from that of monomeric Ru(bpy)32+.

Functicnalization of 4-Hydroxy-6-Methyl-2-Pyrone at C-5 Through [2,3] Sigmatropic Rearrangements of Allylic Sulphonium Ylides

Abstract Functionalization at C-5 of the triacetic acid lactone methyl ether, 7, has been achieved by a transfer from the C-6 position. Thus, treatment of sulfides 12 with an excess of ethyl diazoaceta-te provides the pyrones 15 through [2,3] sigmatropic rearrangements.

ω-Bromoalkapolyenylmethyl ketones—I : Reaction of 5-bromo-3-penten-2-one with triphenylphosphine

Abstract The reaction of (E)-5-bromo-3-penten-2-one with triphenylphosphine affords a 3:1 mixture of two protomeric phosphonium salts 4-oxo 2 pentenyltriphenylphosphonium bromide and 4-oxo-1-pentenyltriphenyl-phosphonium bromide, characterized by the 13C NMR spectrum of the mixture. However, the common phosphorane of these salts gives two condensation products with benzaldehyde, corresponding to α- and γ-condensation respectively.

Synthesis of 5-alkyl-4-bromo-5-hydroxy-2(5h)-furanones and 5-alkylidene-4-bromo-2(5h)-furanones

Abstract Treatment of monoalkylsubstituted allenic esters 4 with NBS and water in the darkness yields β-bromo-γ,β-butenolides 5, that are easily transformed into 5-alkyl-4-bromo-5-hydroxy-2(5 H )-furanones 8 and 5-alkylidene-4-bromo-2(5 H )-furanones 2.

Transient behaviour and luminescence quenching of Rub(bpy)32+ bound to an insoluble polymeric phase

Abstract The spectroscopic behaviour of Ru(bpy) 3 2+ bound to an insoluble polystyrene support is similar to that reported in homogeneous solution and in other heterogeneous media. Following pulsed excitation at 532 nm, emission from the MLCT complex is observed, the decay of which contains both unimolecular and bimolecular components. Weak transient absorption within the sample is also observed and * Ru(bpy) 3 2+ could be identified by its absorption maximum at 375 nm and depletion minimum at 430 nm. Experiments using methylviologen show that luminescence quenching is about forty times slower than in aqueous solution, indicating that the hydrophobic nature of the polymer impedes the approach of the quencher to the ruthenium complex. The inclusion of a hydrophilic sequence in the sample has little effect on improving the quenching efficiency.

Use of selective heteronuclear 13c1h noe measurements. a second note of warning on the assignment of structure to the products formed in the reactions between 4-hydroxy-2h-pyran-2-ones and carbonyl compounds.

Further examples of the occurrence of intramolecular translactonization during condensation of 4-hydroxy-6-methyl-2H-pyran-2-one, 1, or 4-hydroxycoumarin, 4, with carbonyl compounds are desoribed. The structure of previously misassigned products 6a,b is proven by NMR techniques. Application of the HETNOE method to the distinction between structures 9 and 10 is demonstrated.

Synthesis of (+)-Methyl (R,E)-6-Benzyloxy-4-hydroxy-2-hexenoate and Its Mesylate Derivative

Abstract Methyl (E)-6-benzyloxy-4-hydroxy-2-hexenoate is prepared in both racemic and enantiopure form through reaction between (2-benzyloxy)ethyloxirane and the dianion of phenylselenoacetic acid followed by esterification with diazomethane, oxidation to the selenoxide and subsequent pyrolysis in 72% overall yield.

Tandem [2,3]sigmatropic rearrangement of a sulphonium ylide and cyclopropanation of the resulting electron-rich olefin on a 4-methoxy-2-pyrone derivative

Abstract Rhodium catalyzed reaction of 4-methoxy-6-phenylthiomethyl-2-pyrone with dimethyldiazomalonate affords 5-(bis(methoxycarbonyl))(phenylthio)methyl-4-methoxy-6-methylene-5,6- -dihydro-2-pyrone via [2,3]sigmatropic rearrangement of the corresponding sulphur ylide. Cyclopropanation of the 6-methylene double bond occurs by the less hindered side.

Reaction of methyl 2,3-pentadienoate with bromine. Preparation of 4-bromo-5-methyl-5H-furan-2-one

Abstract Treatment of methyl 2,3-pentadlenoate, 3, with bromine in carbon tetrachloride affords a complex mixture, whose main products are methyl ( E )- and ( Z )-3,4-dlbromo-2-pentenoate, 9 and 10, and 4-bromo-5-methyl-5 H -furan-2-one, 4. The mechanism of formation of these and other minor compounds is discussed. Hydrolysis of the crude mixture in the presence of barium hydroxide affords lactone 4 in 30% overall yield.

ω-Bromoalkapolyenylmethyl ketones-II : Use of 5-bromo-3-penten-2-one ethylene ketal as a c5-synthon

Abstract The preparation of the phosphonium salt and the dimethyl-phosphonate of (E)-5-bromo-3-penten-2-one ethylene ketal, 6 and 7, is described. These C5-isoprenoid synthons were condensed with several aldehydes and ketones giving mixtures of the corresponding E and Z-olefination products. Reaction of the anion of the phosphonate derivative with β-ionone gave 9-cis and 9-trans-β-C18-tetraenone ketals, 13 and 14, which by subsequent hydrolysis afforded 9-cis and 9-tras-β-C18-tetraenones, 15 and 16. A C8-isoprenoid synthon is also described.