Leonard E. Houghton
Arizona State University
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Journal of The Chemical Society C: Organic | 1971
George R. Pettit; Leonard E. Houghton
Convenient syntheses of hydroxyhydrolapachol (IIa) and lapachol (I) are reported. Treatment of 2-hydroxy-1,4-naphthoquinone with succinyl peroxide gave the carboxyethyl compound (IVa) which was esterified to give the ethyl ester (IVb). Reductive acetylation of this gave a triacetate (VI) which upon treatment with methylmagnesium iodide, and oxidation of the resulting product, gave hydroxyhydrolapachol. Repeating the reductive acetylation step with hydroxyhydrolapachol followed by treatment with iodine in xylene and saponification led to lapachol.
Journal of The Chemical Society D: Chemical Communications | 1970
George R. Pettit; Peter Brown; Fred Bruschweiler; Leonard E. Houghton
Mass spectral and 1H n.m.r. evidence, coupled with degradation of bufotalin to 3β-acetoxybufotalien (II), in turn prepared by total synthesis, provide unequivocal support for the assignment of structure (I) to bufotalin.
Journal of The Chemical Society D: Chemical Communications | 1970
George R. Pettit; Leonard E. Houghton; John C. Knight; Fred Bruschweiler
A new total synthesis of resibufogenin and bufalin using digitoxigenin, represents the first chemical transformation of a cardenolide to a bufadienolide.
Journal of The Chemical Society-perkin Transactions 1 | 1980
Francis M. Dean; Leonard E. Houghton; Rassoul Nayyir-Mashir; Chachanat Thebtaranonth
Diazoethane adds to 2-methyl-1,4-naphthoquinone giving mainly one regioisomeric pyrazoline (5a) as a mixture of epimers at position 3. The other regioisomer was detected and a related compound (7) was obtained from a similar reaction with diazomethane. The pyrazoline (5a) is transformed into the carbanion (3b) with base and thence into the butylenediquinone (9). Thermal decomposition affords 2-ethyl-3-methyl-1,4-naphthoquinone. Treatment with methanolic base and 2-methyl-1,4-naphthoquinone gives the fluorene derivative (11a) not the expected alcohol (12). Treatment with methanolic base and trimethyl-1,4-benzoquinone affords the expected xanthen derivative (16) but the congeneric fluorene alcohols differed regiospecifically from those observed in other series. One (14) has a cis-fused nucleus; the other is believed to be the trans-fused analogue (13), another departure from previous experience. On the other hand, the reaction with 2,5-dimethyl-1,4-benzoquinone leads to the cage tetraketone (17a) as expected.
Journal of The Chemical Society-perkin Transactions 1 | 1976
Francis M. Dean; Keith B. Hindley; Leonard E. Houghton; Malcolm L. Robinson
Oxidation of the complex naphthol derivative (Ia) by iron(III) chloride in ethanol gives the 1,2-naphthoquinone derivative (III) through loss of the aromatic methyl group. There is an intermediate stage which is reached quickly and appears to give a mixture of products including the stereoisomeric spirans (XIX). Though there are some differences, a general similarity is pointed out between these reactions and oxidations to quinones and spirans in the tocopherol series. No specific precursor was identified.
Journal of The Chemical Society, Chemical Communications | 1979
Francis M. Dean; Leonard E. Houghton; Rassoul Nayyir-Mazhir; Chachanat Thebtaranonth
Generated in methanol under controlled basicity, carbanions react with 2,5- or 2,6-dimethyl-1,4-benzoquinone to give cage tetraketones related to 1,4,7-[1]-ethyl[2′]ylidenenaphthalene or to benz[1,2-a; 3,4-g]-azulene.
Journal of The Chemical Society-perkin Transactions 1 | 1974
Robert Clinging; Francis M. Dean; Leonard E. Houghton
Diazoethane partly alkylates 3-acetylcoumarin giving 3-acetyl-4-ethylcoumarin, and partly expands the lactone ring giving, after addition of a second molecule of diazoethane, the benzoxepinopyrazoline (IX) as a racemate of assigned stereochemistry. This compound readily loses nitrogen and undergoes a second ring expansion to form the benzoxocin derivative (XII) as a single (racemic) stereoisomer. Treatment of (XII) with diazoethane induces immediate ring expansion giving the benzoxonin derivative (XIII), again as a single (racemic) stereoisomer. There is no further reaction with diazoalkanes, notwithstanding the presence of a highly activated double bond; the resistance is attributed to the internal compression that would result within a highly convoluted molecule if addition occurred.The structures and conformations of the foregoing products and of some by-products have been established by spectroscopic methods. Additionally, the benzoxocin derivative (XII) has been shown to yield meso-dimethyl-succinic acid upon exhaustive ozonolysis, and a convenient method is described for the preparation of small amounts of dimethylmaleic anhydride by the reaction of diazomethane with methylmaleic anhydride.A parallel is drawn between these reactions and certain of those found with quinone–diazoalkane adducts, and it is suggested that ring expansions are observed because the methyl group introduced with the diazoethane molecule forces the pyrazoline into the necessary conformation.
Journal of The Chemical Society C: Organic | 1971
Francis M. Dean; Keith B. Hindley; Leonard E. Houghton
In methanol containing sodium hydroxide the xanthen derivative (II) forms a carbanion that adds (reversibly) trimethyl-1,4-benzoquinone giving a derivative (IVa) of bicyclo[3,2,1]octane. Addition of 2-methyl-1,4-naphthaquinone gives a similar derivative (Xa). The structures and stereochemistry of these compounds have been established by a combination of chemical and n.m.r. spectroscopic methods and (IVa), for example, shown to be (7aR*, 11R*, 11aS*, 13R*, 14R*)-8,11,11a,13,14,15,18-heptahydro-5,11-dihydroxy-6,9,10,11a,13,16,17-heptamethyl-7a(7H),11-o-benzenobenzo[c]xanthen-8,15,18-trione.
Journal of The Chemical Society C: Organic | 1970
R. Clinging; Francis M. Dean; Leonard E. Houghton
Diazomethane rapidly converts 3-acetylcoumarin, 3-cyanocoumarin, and their derivatives into the related 4-methyl-coumarins. Since an acetyl group must rotate out of the plane of conjugation to allow the methyl group to enter, it is a less effective activating substituent than cyanide in alkylation reactions.Substituents at the 5-position interfere with the methylation process so that 3-acetyl-5,7-dimethylcoumarin adds diazomethane giving a pyrazoline derivative (XIII) in the usual way. Methanol converts this pyrazoline into oxepin lactones, e.g. 3-acetyl-4,5-dihydro-4-methoxy-6,8-dimethyl-1-benzoxepin-2(3H)-one (XVIII). Thermolysis of the pyrazoline is unusual in regenerating some of the coumarin from which it was made; the main product, however, is a labile substance giving 3-acetyl-6,8-dimethyl-1-benzoxepin-2(3H)-one (XVII) when isolation was attemptedAt –40° diazomethane and 3-acetyl-5,6-benzocoumarin give 1,11c-dihydro-3a-(2-methyloxiranyl)benzo-[5,6]chromeno[3,4-c]pyrazol-4(3aH)-one (XXIV), but at 0° the sole isolable product is 8a-acetyl-11a,12-dihydro-11H-naphtho[1′,2′:6,7]oxepino[3,4-c]pyrazol-8(8aH)-one (XXII).These results support the view that the ‘direct’ methylation begins with an intermediate or transition state having the shape of a pyrazoline but at least one bond which is as much ionic as covalent in character. It continues with hydrogen migration because this restores the delocalisation energy of the coumarin system lost during the addition. The arguments also clarify some of the reasons for cyclopropane ring formation in certain related series.
Journal of Organic Chemistry | 1970
George R. Pettit; Leonard E. Houghton; John C. Knight; Fred Bruschweiler