Photosensitized Oxygenation of Abieta‐7,9(11)‐dien‐13β‐ol

Abstract

SummaryDehydration of abiet-8-ene-7/i, 13P-diol (ibozol, 1) leads to abieta-7,9 (1 1)-dien-13B-01 (2) which aromatizes slowly to the known abieta-8,11,13-triene (3). Photosensitized oxygenation of the heteroannular diene 2 yields a mixture from which three compounds were identified: abiet-7-ene-9n, 11 a , 13P-trio1 (4), abieta-8,11,13-trien-7-one (5), and abieta-8,11, 13-trien-7 u-01 (6).Introduction. -There is considerable interest in the potent anti-leukemic activity and cytotoxicity of certain naturally occurring oxygenated diterpenes [ 1-31 and various synthetic approaches have been recently described [4]. In view of our interest in potential anti-tumoral agents, we report on the photosensitized oxygenation of the previously unknown heteroannular diterpene, abieta-7,9 (1 I)-dien-13 /3-01 (2), prepared from ibozol (1, abiet-8-ene-7b, 13P-diol) a diterpene isolated from the Labiatae Zboza riparia NE BROWN [5]. The photosensitized oxygenation of simpler substrates is well known [6] but few examples are documented in the diterpenoid series [7].

Novel Domino Reactions for Diterpene Synthesis

“…Acid 11 was then subjected to concentrated H 2 SO 4 promoted domino alkylation-cycloacylation with anisole (12) to yield the tricyclic ketone (22), which was subsequently transformed, as depicted in Scheme 6, to the octahydrophenanthrene (23), which has been previously converted [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] to the antibacterial 16 diterpene, (()-totarol (4).…”

“…Acid 11 was then subjected to concentrated H 2 SO 4 promoted domino alkylation−cycloacylation with anisole ( 12 ) to yield the tricyclic ketone ( 22 ), which was subsequently transformed, as depicted in Scheme , to the octahydrophenanthrene ( 23 ), which has been previously converted − to the antibacterial 16 diterpene, (±)-totarol ( 4 ).

6 Total Formal Synthesis of Totarol (4) via Domino Alkylation-cycloacylation.

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