ChemInform Abstract: The Regioselective Bromination of 4,4-Dimethyl-5,8-dihydroxy-4H-naphthalen-1-one (original) (raw)
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Novel cycloaddition reactions of o -benzoquinones and related chemistry
Journal of Chemical Sciences, 1998
o-Benzoquinone is a unique conjugated 1,2-dione that can exhibit diverse cycloaddition modes, participating either as carbodiene, heterodiene, dienophile or heterodienophile. With electron-rich dienes, benzodioxins are formed in excellent yields. Pentafulvenes including 6-vinylfulvenes normally give rise to bicyclo[2.2.2] adducts. Exceptions are observed with cycloalkylfulvenes where the fulvenes undergo rearrangement to cyclopentadiene derivatives prior to cycloaddition, resulting in be .ngodioxins. o-Benzoquinones participate as dipolarophiles on treatment with nitrile o~des and carbonyl ylides yielding highly oxygenated novel spiro compounds. Triphenylphosphine catalyzed addition of DMAD to o-benzoquinones afforded another class of novel spirolactones. The bicyclo[2.Z2] octene diones derived from o-benzoquinones undergo a number of synthetically useful transformations.
The formal oxidative addition of electron-rich transoid dienes to bromonaphthoquinones
The Journal of Organic Chemistry, 1991
This work established the idea that a halogen atom, such as bromine, will act as a control element in the regiospecific formation of a new carbon-carbon bond. The addition of the electron-rich end of a traneoid diene to a bromojuglone derivative occurred exclusively a t the unsubstituted carbon of the quinone. Thus, 2,2-dimethyl-4-methoxy-6-methylene-1,3-dioxa-2-sila-4-cyclohexene (3) and either 2-or 3-bromo-5-hydroxy-l,4naphthoquinone (1 or 2) afforded the adducts 19 or 20 in 57% or 71% yield. Similarly, 2,2-dimethyl-6methylene-4-(trimethylsiloxy)-l,3-diox-4-ene (4) and 1 gave 21 in 77% yield.
Bioorganic Chemistry, 1989
During the oxidation of dihydrocaffeic acid catalyzed by mushroom tyrosinase, the corresponding quinone formed undergoes an unusual nonenzymatic intramolecular nucleophilic addition reaction yielding dihydroesculetin. This compound was further converted to the oquinone which accumulated in the reaction mixture. Chemically synthesized dihydrocaffeiyl quinone also exhibited the same lactonization reaction. The product of the reaction was isolated and characterized by uv, ir, and NMR spectra1 studies. One of the minor products of enzymatic oxidation was identified to be caffeic acid. Since intramolecular cyclization dominated side chain desaturation, methyl ester of the parent acid was substituted in the tyrosinase reaction in order to suppress the cyclization route and monitor the side chain desaturation. Such studies readily generated methyl caffeate as the major product of tyrosinase-catalyzed oxidation of dihydrocaffeate methyl ester. The formation of this product was accounted for by a novel nonenzymatic route involving tautomerization of enzymatitally generated dihydrocaffeiyl quinone to its quinone methide and subsequent aromatization of the latter. The above results indicate that (a) even weak nucleophiles such as carboxylate can react with quinones to form esters and (b) suitably substituted quinones undergo spontaneous quinone methide formation and rearrange further to yield Q-unsaturated catechols as stable products. The significance of these reactions for sclerotization of insect cuticle is discussed.
Canadian Journal of Chemistry, 2000
The intramolecular Diels-Alder reaction of furanyl amides derived from 2-furylacetic acid has been examined. Substrates containing either an imide or tertiary amide linkage between the furan and the dienophile underwent smooth cycloaddition upon thermolysis. By varying the reaction conditions, either the primary cycloadduct or the ringopened and acetylated product could be isolated in excellent yield. The stereochemical outcome of the IMDAF cycloaddition has the side arm of the tethered alkenyl group oriented syn with respect to the oxygen bridge. Semiempirical AM1 calculations show that the exo-cycloadduct is 11 kcal lower in energy than the corresponding endo adduct and, presumably, some of this energy difference is reflected in the transition state for the cycloaddition. The IMDAF reaction of N-allyl- [2-(3,4-dimethoxyphenethyl)]-2-furanyl-2-yl-acetamide proceeded in 90% yield upon heating in xylene. The 4+2-cycloadduct undergoes ring-opening on treatment with base and the resulting alcohol was converted into the corresponding benzyl ether. Raney nickel reduction followed by Bischler-Napieralski cyclization furnished the tetracyclic skeleton of the berberine alkaloids.