Abstract
Two synthetic pathways have been developed which lead to the natural product cleistopholine (1). One route has been adapted for the synthesis of the methylated analogues 2 and 3. The key step involved nickel-catalyzed regiospecific coupling of benzylic zinc bromides with methyl-2bromo-4-methyl nicotinate (10) to afford benzylated pyridines followed by their subsequent transformations to the benzo[g]quinoline-5,10-diones.
Highlights
Prepared from 14b by modification of Method A to yield 2 (33%) as a yellow solid which quickly darkened on standing in air; mp 210-212 oC; 1H NMR (CDCl3) δ 8.89 (d, J = 4.8 Hz, 1H), 8.26 (d, J = 7.9 Hz, 1H), 8.06 (s, 1H), 7.61 (d, J = 7.9 Hz, 1H), 7.48 (d, J = 4.7 Hz, 1H), 2.91 (s, 3H), 2.55 (s, 3H)
Cleistopholine (1) is a naturally occurring benzo[g]quinoline-5,10-dione which has been isolated from the root bark of Cleistopholis patens (Annonceae),[1] the stem bark of Oncodostigma monosperma (Annonaceae),[2] the trunk bark of Meiogyne virgata polyalthia (Unoneae)[3] and the fruit seeds of Annona cherimolia.[4]
The synthetic pathway is illustrated in Scheme 1
Summary
Prepared from 14b by modification of Method A to yield 2 (33%) as a yellow solid which quickly darkened on standing in air; mp 210-212 oC; 1H NMR (CDCl3) δ 8.89 (d, J = 4.8 Hz, 1H), 8.26 (d, J = 7.9 Hz, 1H), 8.06 (s, 1H), 7.61 (d, J = 7.9 Hz, 1H), 7.48 (d, J = 4.7 Hz, 1H), 2.91 (s, 3H), 2.55 (s, 3H).
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