Quinol, Epoxy

From the hind gut of Cetonia aurata an Actinomyces species was isolated which produces the new cytotoxic epoxy quinoles [190] named cetoniacytone A 90 and B 91. In addition, the structurally related aromatic compounds 2,5-di-hydroxy-4-hydroxymethylacetanilide 92 and 2,5-dihydroxy-4-methoxymeth-ylacetanilide 93 were found in minor amounts. 

The extremely broad functional group tolerance of the Pd-catalysed N-de protection of Aloe groups was a crucial design feature in a synthesis of the epoxy-quinol core of the Manumycin family of antitumour antibiotics [Scheme 8,80].195 Note the convenient generation of the Pd(0) catalyst in situ from reaction of dichlorobis(triphenylphosphine)palladium(II) with tributylstannane. The use of sodium borohydride and borane dime thy lamine complex is illustrated in Schemes 8.81193 and 8.82194 respectively. 

Upon wanning, the epoxy-p-quinols 3 were obtained. Interestingly, when the p-hy-droperoxide was dissolved in DMF containing t-BuOK, most of 2 reverted instantaneously to 1 with the liberation of oxygen. This indicates the reversibility of the dioxygen addition and the inherent instability of the peroxy anions in absence of suitable solvation. 

A synthesis of bistetrahydroisoquinolines using p-quinol acetate 3 and 8,8a-epoxy p-quinol 495 was performed (130-132). Reaction of 3 cory-palline (1) (130), isocorypalline (4), and 6- and 7-tetrahydroisoquinolinols (131) and subsequent acetylation gave substituted bistetrahydroisoquinolines 487-492 (Scheme 64). Interestingly, similar treatment of 3 with... 

Geissospermine. (t6R,l9E)-l9,20-Didehydro-[6- (lQptt) 2l )-23-deoxy-2JI 22 dihydro-If-oxa"12t 14-seco-strych nidin-I Q-ylJcarynan 17-oic acid methyl ester 19 20 didehydro-16-(15-ethyl-3at f a 7t8.l3a-hexahydro-4H-4r6-ethan o-lH,3H [l,3Joxa zino[S,4y 5 1 mJpyrrolof2,3-dJca rbazol-l-yl)-corynan-l7-oic acid methyl ester 0,l7-epoxy- t-(3-ethylidene-1,2,3,4,6,7.12, I2b-octahydroindole[2,3-a]quinol-izin -2 -y0-curan-1 -propanoic acid methyl ester. 

Preparation.—Catalytic Oxidation of Alkenes to Oxirans, using Oxygen or Oxygen-containing Gases. The mechanism for the conversion of the phenol (1) into the epoxy-quinol (4) by molecular oxygen in Bu OK-Bu OH has been investigated (Scheme 1)." The first step is the formation of hydroperoxide (2), which is converted into hydroperoxide (3) via a -n--complex intermediate the yield of (4) increases with temperature. 

In protic solvents a different regioselectivity is observed. Oxygenation of 1 in t-butanol leads predominantly to the o-peroxyphenolate intermediate 6, which is further converted to epoxy-o-quinol ... 

Base-catalyzed ring opening of 8 produces an enolate anion, which leads to ring contraction. At room temperature the reaction stops at the epoxy-o-quinol stage (8). 

Co OH converts the starting phenol to the phenolatocobalt(111) species 24, which may be formulated as a 7r-complex. The free phenolate anions of 1 give only epoxy-p-quinols [11,12], which are distinctly different from the products in the presence of metal ions. 

Nishinaga, A., T. Shimizu, and T. Matsuura Base-catalyzed Oxygenation of tert-Butylated Phenols 3. Base-catalyzed Reaction of Peroxyquinols Derived from Oxygenation of 2,6-Di-tert-butylphenols and Mechanism of Regioselective Formation of Epoxy-o-quinol from 2,4,6-Tri-tert-butylphenol. J. Org. Chem. 44, 2983 (1979). 

---