1059. The base-catalysed isomerisation of some 3-alkyldi-hydronisoles

Abstract

Isomerisation with sodamide in liquid ammonia of the S-alkyldihydroanisoles (IV) containing unconj ugated double bonds gives the exocyclic conjugated dienes (VI) as the final product if R'Reduction by sodium and propan-2-01 in liquid ammonia of 3,4-dimethylanisole (VII) and of B-methoxy-1,2,3,4-tetrahydronaphthalene (IX), followed by similar isomerisation, gives the endocyclic dienes (VIII) and (X). The mechanisms involved are discussed.REDUCTION of alkylanisoles with sodium and ethanol in liquid ammonia gives chiefly dihydroanisoles containing unconjugated double bonds as the result of kinetically controlled reactions.l~~*~ In the presence of an alkali-metal amide in liquid ammonia, these dienes are converted into the more stable conjugated isomers, usually by turning of a double bond about the carbon atom bearing the methoxyl group. This has been shown 3 ~4 to be due to establishment of an equilibrium of the type shown below. Apart from their intrinsic interest, a study of such reactions is important in understanding the course of reductions by lithium and various amines, since such equilibrations are clearly involved and permit reduction to occur past the dihydro-stage.2 H 6 Because 2,5-dihydroanisole is converted into 2,3-dihydroanisole as above, it was expected that 2,5-dihydro-3-methylanisole (I) would give the homologue (11). In fact this is produced to some extent, as shown by the diene reaction with dimethyl acetylenedicarboxylate.6 However, it was noted 6 that if the isomerisation proceeded for a long time, and in particular if the ammonia evaporated, a different product was obtained. This has now been shown to be the exocyclic diene (111) and it has been found that the endocyclic diene (11) cannot be prepared by this method in a state of purity because its rate of isomerisation to the diene ( 111) is comparable with its rate of formation.The courses of these and analogous reactions were followed by means of ultraviolet spectra. The unreduced alkylanisoles have twin peaks,' A , ,

Strategic synthesis based on cyclohexadienes: preparation of 2-, 2,3- and 2,4-substituted cyclohexenones; synthesis of (Z)-heneicosa-6-en-11-one

“…Eschenmoser's fragmentation cia the tosylhydrazone to the acetylenic aldehyde (9). Further elaboration of the chain was accomplished through the Grignard addition with decylmagnesium bromide and the resulting alcohol (10) was oxidised to the acetylenic ketone (11). Partial hydrogenation of the ketone (11) with Pd-BaS04 gave the pheromone (12) in good yield (overall 22%), the spectral data of which were identical with the published data.…”

Conversion of some dihalogenocyclopropanes into unsaturated ketones

“…Dichloronorcarane was reported to react with concentrated sulphuric acid, giving hydrogen chloride and resinous products. 6 We find that dibromocarbene adducts of cyclic olefins react cleanly at room temperature with a concentrated solution of silver sulphate in 98% sulphuric acid, the latter also serving as a good solvent for both reactants. Precipitation of silver bromide occurs rapidly and is usually complete in 24 hr.…”

“…It gave a 2,4-dinitrophenyZhydrazone forming orange-red crystals from ethyl acetate, rn. p. 16&-170° (Found: C,36.4;H,[2][3][4][5][6][7]Br,N,12.3. C,4H,2Br,N,0,requires C,36.5;H,2.6;Br,; N, 12.2y0), (CHC1,) 370 mp, ( E 29,000).…”

New chemical and stereochemical applications of organoiron complexes

“…Reaction of 1,4-cycIohexanediene (readily available from the Birch reduction of benzene or its derivatives) [ 109 ] or 1,3-cyclohexanediene with pentacarbonyliron [Fe(CO) 5 ] gives tricarbonyl (1,4- or 1,3-cyclo-hexanediene) iron complexes [ 14 , 20 , 109 – 112 ]. These complexes readily undergo hydride abstraction by treatment with triphenylmethyl (trityl) hexafluorophosphate or tetrafluoroborate in dichloromethane, to give tricarbonylcyclohexadienyliron hexafluorophosphate (or tetrafluoroborate) as stable, dull-yellow salts [ 32 ], e.g., metal-stabilized cyclohexadienyl cations [ 110 – 112 ].…”