R.D.H. Murray

Claisen rearrangements—II : Synthesis of six natural coumarins

Abstract Pyrolysis of the natural coumarin, 1 , has been shown to give obliquetin, 2 , nieshoutin, 3 , and the out-of-ring rearrangement product, 10 . Methylation of 10 gave rutacultin, 11 . A convenient preparation of 1 and scopoletin, 6 , from aesculetin, 5 , is described.

Claisen rearrangements—III : Convenient syntheses of the coumarins, osthenol, demethylsuberosin and coumurrayin

Abstract A simple 3-step method for the introduction of a 3,3-dimethylallyl unit ortho to a phenolic OH group is described. 7-Hydroxycoumarin, 1, was converted to its 1,1-dimethylallyl ether, 5, by reaction with 3-chloro-3-methylbutyne followed by partial hydrogenation. Pyrolysis of 5 gave mainly the C-8 Claisen rearrangement product, osthenol, 10, and also the C-6 isomer, 14. In a similar manner, coumurrayin, 13, was prepared from 5-methoxy-7-hydroxycoumarin in 57 % overall yield.

Claisen rearrangements-IV : Oxidative cyclisation of two coumarin o-isoprenylphenols

Abstract Osthenol ( 1 ) has been found to react quantitatively with m -chloroperbenzoic acid in EtOAc or ether to furnish only the dihydrofuranocoumarin. (±)-columbianetin ( 6 ). When CHCl 3 acidified with HCl was used. the sole product was the dihydropyranocoumarin, (±)-lomatin ( 7 ). In a similar manner. 7-demethylsuberosin ( 8 ) was converted into (±) marmesin ( 13 ) and (±) decursinol ( 14 ).

Constituents of Solidago species—I: The constitution and stereochemistry of diterpenoids from Solidago canadensis L.

The constitution and stereochemistry of solidagenone II and the epimeric spiro ethers III from Solidago canadensis L. are deduced from their spectroscopic and chemical properties.

Claisen rearrangements—VI : Synthesis of the coumarins, sesibiricin and toddaculin

Abstract The natural coumarins, sesibiricin ( 1 ) and toddaculin ( 28 ) have been synthesised from 5,7-dihydroxycoumarin, the former by a sequence involving regioselective O-prenylation at C-5 and C-prenylation at C-8. The prenyl ether of 5-hydroxy-7-methoxycoumarin, a key intermediate in the synthesis of toddaculin, has been found to undergo Claisen rearrangement exclusively to the para position thereby providing an alternative route to sesibiricin.

Claisen rearrangements—I : Synthesis of the coumarin, pinnarin

Abstract The natural coumarin, pinnarin (9) has been synthesised in four steps from 5. Introduction of the 1,1-dimethylallyl unit at C-8 has been achieved in high yield by performing the Claisen rearrangement of the 3,3-dimethylallyl ether (6) in the presence of butyric anhydride. Unusually strong OH-π intramolecular H-bonding is observed in the IR spectrum of 8.

Infrared studies of chromones—I : Carbonyl and hydroxyl regions

Abstract Quantitative IR solution data in carbon tetrachloride and chloroform are recorded for the CO and OH regions of 31 chromones. In the 1580–1700 cm −1 region, 5-hydroxychromones show three main maxima, the two of highest frequency, at 1663 ± 3 cm −1 and 1630 ± 5 cm −1 in CCl 4 (1661 ± 2 cm −1 and 1627 ± 5 cm −1 in CHCl 3 ), being sufficiently intense as to possess high CO character. Typically, 5-alkoxychromones exhibit two intense maxima in this region, 1663 ± 3 cm −1 and 1613 ± 7 cm −1 in CCl 4 (1657 ± 2 cm −1 and 1608 ± 12 cm −1 in CHCl 3 ). Diagnostically useful changes in contour and principal peak positions can be seen for substituted and annellated 5-hydroxychromones. In the 2500–3650 cm −1 region, the stretching frequencies of OH groups at the most commonly encountered positions (C-5, C-7, and 2-CH 2 OH) in natural chromones, are identified.

Claisen rearrangements—VIII1: Synthesis of the coumarins, avicennol, dipetaline and dipetalolactone

Abstract The structures of the natural coumarins, avicennol (1) and dipetaline (2) have been confirmed by an unambiguous synthetic route from 5,7-diacetoxycoumarin. This sequence, initiated by a regiospecific O-prenylation at C-5, contains a rearrangement step which introduced the 3-methylbut-2-enyl group exclusively and in high yield at C-8. Insertion of the chromene ring gave dipetaline which on photo-oxygenation-reduction afforded avicennol as sole product. The synthesis of the dipyranocoumarin, dipetalolactone (  hortiline) (19) has also been effected.

Claisen rearrangements—VII : Novel reactions of the coumarin, tomentin☆

Abstract The structure of tomentin has been confirmed as 5-hydroxy-6,7-dimethoxycoumarin (2), the derived 3,3-dimethylallyl ether giving a para-Claisen rearrangement product. Relief of strain in the corresponding 1,1-dimethylallyl ether has been found to result in a novel regiospecific ortho-Claisen rearrangement occurring on silica at room temperature. The structure 18 of the stable ortho-dienone formed has been confirmed by conversion of the corresponding dehydrodienone (15), obtained from the rearrangement of tomentin 1,1-dimethylpropargyl ether, to alloxanthoxyletin (25).

Infrared studies of chromones—II : Isotopically substituted 5-hydroxychromones

Abstract By deuteration of the OH group, it has been shown that two bands, at ∼ 1665 and ∼ 1630 cm−1 (CCl4), in the IR spectra of 5-hydroxychromones are associated with the H-bonded CO stretching vibration. Nuclear deuteration of 5-hydroxy-2-methylchromone (1) under acidic conditions gave a tri- and a hexadeutero derivative; the latter, isotopically substituted at C-3, shows a single CO band at 1649 cm−1. Hydrolysis of 3-acetyl-5-hydroxy-2-methylchromone with sodium carbonate in deuterium oxide furnished 5-hydroxy-2-trideuteromethylchromone-3-d which also exhibits a single CO absorption. Partial incorporation of O18 into the CO group of 1 results in a single νCO18 at 1593 cm−1. It is suggested that the doublet CO absorption of 5-hydroxychromones arises from a Fermi resonance involving a low-energy vibrational mode of the vinyl proton on the nuclear C-3 position.