The Structure of Secalonic Acids A and B

Abstract

equilibrium mixture of ( I ) , (2) and (3); compound (5) was rearranged, with a 1,s-homodienyl hydrogen shift [3], into bicyclo[3,3,0]octa-2,7-diene. The photolysis of (3) gave rise to ( 4 ) , (5), and (7)-(10).The formation of (4) and (5) in 22 and 10 yields indicates that they originate from (2) which occurs as an intermediary product. This assumption could be supported by photolysis of 5,8-dideuterocycloocta-1,3,6-triene (3a). Its product of isomerisation (4u) showed a distribution of deuterium which corresponds t o an isomerization (3) + ( 2 ) , by way of a 1,5-hydrogen shift [4]. Compound (7) was forme&, on the other hand, without hydrogen shift: The product (7. ) which was obtained on photolysis of (-?a), carries deuterium only at C-4 and C-8. It is suggested that its formation is due to a rearrangement of the santonine type [5]. The 1,2-homotropilidene (11), which would also be expected, is converted to (8) under the conditions of experiment. ( 1 1 )Open-chain 1,3,6-trienes can be isomerized in the same way.Thus 5,5-dimethylhepta-l,3,6-triene is readily rearranged on irradiation into a mixture of cis-and trans-3,3-dimethyl-l,2divinylcyclopropane [6]. The structure of (10) was deduced from infrared and N M R spectra. The formation of (10) is the first example of a photochemically induced Diels-Alder reaction. Received, March 12th, 1964 [Z 693/534 IE] German version: Angew. Chem. 76, 378 (1964)

Vinylogous Addition of Siloxyfurans to Benzopyryliums: A Concise Approach to the Tetrahydroxanthone Natural Products

“…The recently isolated tetrahydroxanthones blennolides A ( 1 ) and B ( 2 ) (Figure 1)2 are monomer units of the antitumor agents secalonic acids B ( 3 ) and D ( 4 ),3 the latter which exhibits antibacterial, cytostatic, and anti-HIV properties 4. Blennolide C ( 5 ), the methyl isomer of 1 , and the antifungal agent parnafungin A ( 6 )5 also possess the characteristic dihydro- 2H -xanthenone framework found in many tetrahydroxanthones.…”

Asperbenzophenone A and Versicolamide C, New Fungal Metabolites from the Soft Coral Derived Aspergillus sp. SCSIO 41036

“…Therefore, the absolute configuration of 5 is the same as that of 6 with the configuration 3R,11R,17R,21S. The known compounds were elucidated as 2,2',6'trihydroxy-4-methyl-6-methoxy-acyl-diphenylmethanone (2), [12] 2,2',6'-trihydroxy-4-hydroxymethyl-6-methanol-acyl-diphenylmethanone (3), [15] emodin (4), [16] (À )-versicolamide B (6), [14] secalonic acid A ( 7), [17] penicillixanthone A (8), [18] 7-hydroxy-3-(2-hydroxypropyl)-5-methyl-isochromen-1-one ( 9), [19] 2,5-dimethyl-7-hydroxychromone (10), [20] methyl indol-3-ylacetate ( 11), [21] (E)-12-hydroxyoctadec-10-enoic acid (12), [22] asperidine C (13), [23] L-657,398 ( 14), [24] chrysogeside E (15), [25] AGE-1 ( 16) and AGE-2 (17) [26] by comparison of their MS and NMR data with those reported in the literature.…”

Concise and Stereodivergent Approach to Chromanone Lactones through Copper‐Catalyzed Asymmetric Vinylogous Addition of Siloxyfurans to 2‐Ester‐Substituted Chromones

“…Using Porco's protocol, [4] treatment of 8 with NaH in THF afforded (À )-blennolide B (9) (19 % overall yield 5 a), whose spectroscopic characteristics were identical to those reported. Secalonic acid A [21] could also be accessed using 9 based on Porco's approach. [5a] In summary, we have developed an asymmetric coppercatalyzed process that delivers enantioenriched chromanone lactones with catalyst-controlled diastereodivergence for formation of elusive tetra-and tri-substituted stereocenters.…”