Synthesis and Structure of a Linearly anti‐Annelated Tetracycloundecane. A Potential Precussor for a Coriolin Synthesis

Abstract

tion of 2,3-dimethyl-2-butene further confirmed its identity as lo2.After correction for differing sensitizer optical densities, the maximum intensities of 1and 2-sensitized '02 luminescence were compared. Since the quantum yield of triplet formation from 2 is 0.81[51, and this state is efficiently quenched by oxygen to form 'Oz[51, the absolute quantum yield of cercosporin-sensitized formation of 'Oz could be determined. Based on four independent determinations, the relative ratio of luminescence produced from 2 to that produced from 1 was found to be 1.01f0.04. Two separate determinations of the relative rates of photooxygenation of 2-methyl-2-pentene in benzene sensitized by 2 and 1 gave the ratio 1.00-+0.12. Both ratios indicate that the quantum yield of formation of '02 sensitized by 1 is 0.81 f 0.07.This large quantum yield strongly supports the suggestion that singlet oxygen is the toxic agent in host plants. This is a striking example of the use of a chemical mechanism by a parasite to gain an "environmental advantage". . Chem. Soc. Farad. Trans. I 76 (1980) 852.[6] Cercosporin was provided by Dr. M. E. Daub, Michigan State University.Its structure and purity were confirmed by comparison of the absorption and NMR spectra with published data"'. 2-Methyl-2-pentene (Aldrich) was purified by column chromatography on basic A1203. C6H6 (Mallinckrodt) was distilled from P20, immediately before use. 2 (Sigma) and C6H6 (Cambridge Isotope Laboratories) were used as received.-The apparatus used to observe '02 luminescence has been described previously 141.Dedicated to Professor Giinther 0. Schenck on the occasion of his 70th birthdayWe recently presented a widely applicable concept for the synthesis of cyclopentanoid natural products based on the utilization of tricyclo[3.3.0.02~8]octan-3-one 1 as central optically active building block"*21. Scheme 1 outlines the strategy (AB + C principle) now chosen by us for the preparation of the tetracycloundecanes 9 and 12, which are potential precursors for the synthesis of coriolins"'. The most important step in the sequence involves the previously only indirectly dernon~trated~~' anti-annelation of a third five-membered ring to 1. tion of the rings A and C in 13 could be confirmed by an X-ray structure analysis. ie H U 9 lh -0 L 10

Novel Variant of the Tricyclooctanone Approach to Cyclopentanoid Natural Products. Synthesis of (±)‐Coriolin. Preliminary Communication

“…The product mixture could be used directly in the subsequent alkylation, in which 3a/3b yielded the single product 47, and 10a/10b were decomposed under the alkaline conditions. For the alkylation (of 3a/3b) and the oxidative cleavage (of 5) to 6')7'), conditions described earlier [6] for related transformations were applied. The intervening Birch reduction 4-Sa) was highly selective with respect to both the regiochemistry of the cyclopropane cleavage (opening between C(2) and C(8)) and the stereochemistry of the C(6) ketone reduction to the thermodynamically favored 'exo' hydroxyl group').…”

“…We have previously demonstrated that the use of the optically active forms of tricyc1o[3.3.0.0*~*]octan-3-one provides for a versatile synthetic approach to cyclopentanoid natural products [3] [5] [6], including one towards the total synthesis of coriolin, (-)-(9) [6]. Scheme 1 summarizes an alternative to this concept which is characterized by an unprecedentedly short route to the intermediate 8 in common with previous total syntheses of (f)-coriolin (9) [2].…”

“…For the base-catalyzed ring closure 6-+7")), known procedures [I] [2] previously applied in related work [6] were adopted. The sequence was completed by treatment of the dienol acetate derivative of 7 with oxone [ 1 I] to give a product which was identified with an authentic sample of 177, 162, 135, 109, 55, 43 (base peak).…”