The condensation of hydroquinone ethers with an excess of dihalomaleic anhydrides has been found to give particularly good yields of dihalonaphthazarins. The etherification of the latter and the nucleophilic substitution of 2,3-dichloronaphthoquinones have been examined. Finally the structures of the products obtained from the Fries rearrangement of polyacetoxynaphthaIenes have been definitively established.La condensation d'Cthers d'hydroquinones avec un excirs d'anhydrides dihalogCnomalCiques donne des rendements particuliirrement ClevCs en dihalogCnonaphtazarines. La mCthylation de ces substances et la substitution nuclCophile de dichloro-2,3 naphtoquinones ont Ct C Ctudikes. Enfin la structure des produits obtenus lors d e la transposition d e Fries de polyacCtoxynaphtal&nes a CtC Ctablie de f a~o n dCfinitive.Can. J. Chern., 52,838 (1974) Few methods exist for the formation of naphthazarins and none of these are very satisfactory. The syntheses of substituted compounds of this type (whether natural or otherwise), in spite of their apparent simplicity, are therefore usually quite tedious processes. We have attempted to improve the preparation of the basic structure and in principle render its derivatives more readily accessible. The Preparation and Structure of Dihalonaphthazarins and of the Corresponding EthersSince its discovery by Zahn and Ochwat (l), the preparation of naphthazarins by the condensation of hydroquinones (or their ethers) (2) and maleic anhydrides in a molten mixture of aluminum and sodium chlorides has been frequently used. This method remains the most simple way of obtaining many naphthazarins but it suffers the serious inconvenience of giving rather low yields. We have found that the use of excess dichloromaleic anhydride can increase the yield quite spectacularly, in one case to 97%. Stoichiometric amounts of anhydride, dibromomaleic anhydride, and substituted hydroquinones give lower yields. Since the halogens can readily be removed (3), this modification also constitutes a convenient synthesis of some halogen-free naphthazarins.The determination of oxidation-reduction potentials of qninones (4) and the analysis of the n.m.r. spectra of naphthazarins (5) ' have shown that the latter exist mainly in the tautomeric form with the electron-withdrawing groups in the aromatic ring. These results suggest that the predominant tautomer of 2,3-dihalonaphthazarins should be B (Scheme 1). However the n.m.r. spectra of 2a, 2b, and 3 show only one signal at 6 7.33, 7.31, an 7.12, respectively, for ring protons and indicate that these compounds exist mainly with the halogens in the quinoid ring. (The spectrum of 3 could seem ambiguous but is in good agreement with other well established structures such as 6-ethyl-2-hydroxynaphthazarin, F 7.13 (7-CH) (5).) The resonance effects which seem to predominate over other considerations in these cases apparently were not taken into account in earlier works.The etherification of naphthazarins has not been studied extensively. Brass et al. (6) were not abl...
Les auteurs proposent deux nouvelles solutions a u problkme de la synthkse de methyl-3 furoquinones. Ces methodes ont I'avantage de requerir des substrats et des reactifs facilement accessibles. Une nouvelle synthkse de la tanchinone I(26) illustre I'un des procedes qui devraient en principe s'appliquer tgalement a la synthese d'isotanchinones. Au cours de cette etude, quelques transformations inedites ont aussi kt6 observees.The authors propose two new solutions to the problem of the synthesis of 3-methylfuranquinones. The methods have the advantage of requiring readily accessible substrates and reagents. A new synthesis of tanshinone I(26) illustrates one of the processes which in principle should also be applicable to the preparation of isotanshinones. Several novel transformations have been observed in the course of this study.Can. J. Chem., 52,88 (1974) Synthkses de furonaphtoquinones Les quinon-s cornportant un heterocycle oxygtnt ont souvent t t t isoltes de sources naturelles (1) et, puisque certaines proviennent probablernent des composts hydroxylts correspondants, nous avons recherche des rntthodes de synthtse B l'aide de ces intermtdiaires. Depuis le dtbut de ces travaux, un certain nombre de synthtses de mtthyl-3 furoquinones ont Ct C rtalistes (2-4). Nos rntthodes constituent toutefois des proctdts nouveaux et de plus cette ttude nous a perrnis d'observer des rtactions inidites concernant la formation d'alkyl-2 furoquinones.Le problkrne principal, celui de la prtparation de mtthyl-3 furoquinones, a ett abordi par 1'Ctude de la synthtse du dihydro-4,5 mtthyl-3 dioxo-4,5 naphto[l,2-blfuranne (14b). King et Read (5) avaient dtjB obtenu cette substance par une rnCthode qui s'est avtrte inapplicable B la synthtse des tanchinones. La f a~o n la plus directe d'envisager la prtparation consiste sans doute B introduire dans l'hydroxy-2 naphtoquinone (1) une chaine fonctionnaliste susceptible de se cycliser en rntthyl-3 furoquinone. Puisque ce groupement doit contenir trois atornes de carbone, le propanal ou ses derives sernblaient etre des rtactifs tout designts pour optrer cette transformation. Toutefois, des condensations directes entre l'hydroxy-2 ou la chloro-3 mtthoxy-2 naphtoquinone et le propanal en prtsence de NaH ne donntrent aucun rtsultat utile.Une observation inCdite sur la reaction de quinones avec certains halogtnures d'alkyles sernblait offrir quelqu'espoir de succks par la condensation de l'hydroxy-2 naphtoquinone et d u bromo-2 propanal. Une premikre tentative ne conduisit qu'B une faible quantitt de dihydro-4,5 mtthyl-2 dioxo-4,5 naphto[l,2-blfuranne (2) obtenu sans doute par la cyclisation de l'hydroxy-3 (brorno-2 proptny1)-2 naphtoquinone intermediaire, une rtaction analogue B celle observte par Hooker (6). I1 s'agit, B notre connaissance, du premier cas d e condensation de ce genre avec des aldehydes a-halogtnts et d'un exemple rare d e synthtse directe d'une furoquinone B partir d'une hydroxyquinone. Un second assai, effectut avec le m&me aldehyde en prtsence de HBr, donna un melange...
Durch reduktive Acetylierung der Chinone (I) werden die Triacetate (II) erhalten, deren sukzessive Oxidation mit OsO4 und mit NaIO4 die Carbaldehyde (III) liefert.
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