Synthetic studies of the antitumor antibiotic streptonigrin. II. Synthesis of the C‐D ring portion of streptonigrin

Abstract

Partial mclhylalion of gallopropiophenonc (4) followed by benzylation and base‐catalyzed condensation with ethyl acetate yielded 3‐(2‐benzyloxy‐3,4‐din]etlK>xy)benzoyl‐2‐butanonc (6). Animation of the latter and subsequent base‐catalyzed cyclization with ethyl cyanoacetate gave 4‐(2‐benzyloxy‐3,4‐dimethoxy)phenyl‐5,6‐dimethyl‐2‐oxo‐1,2‐dihydropyridine (8). Removal of the 2‐oxo group of 8 through chlorination and dechlorination and stepwise conversion of the 5‐cyano and 2‐methyl groups into the 5‐amino and 2‐carboxylic acid groups, respectively, with introduction and removal of protecting groups at proper stages, yielded the C‐D ring moiety of the antitumor antibiotic streptonigrin.

The total synthesis of streptonigrin and related antitumor antibiotic natural products

“…Wittek, and Cheng (see also Scheme 7), 73 was condensed with methyl acetoacetate to form the 3-acetyl-4-arylpyridone 195. The acetyl group was reduced to the alcohol 196 (possibly a diastereomeric mixture, due to the presence of both central and axial chirality, but not specified) and further converted to the 2-chloro-3-vinylpyridine 197 by using phenylphosphoryl dichloride.…”

Synthesis and properties of 4-(3-amino-2-benzofuranyl)-coumarins

“…The synthesis of substituted 5H-chromeno[3,4-c]pyridin-5-ones has been studied by many workers and various methods have been reported for the preparation of these compounds, including the condensation of 3-cyano-4-(2-hydroxyphenyl)pyridine derivatives in PPA or HBr/HCl [11][12][13][14], of 4-(2-fluorophenyl)nicotinic acid upon heating [15], of salicylaldehyde, malononitrile, or ethyl cyanoacetate and ketones in the presence of ammonium acetate [16][17][18][19][20][21], of 4-dicyanomethylene-4H-1-benzopyrans with amines [22], and of 3-acetylcoumarin with cyanoacetamide and ketones [23].…”

Linking of four acetylene molecules at a dimolybdenum center and the protonation of the resulting metallacyclononatetraene to form a cation containing a bridging MoHC system

“…A rapid reaction occurred affording [Fe2(CO)4(775-C5H5)2] together with a purple crystalline dimolybdenum complex 2. ['H NMR (C6D6) r 4.91 (s, 5 H, C5H5), 6.20 (s, 5 H, C5H5), 7.60 (s, 6 H, Me), 7.75 (s, 6 18.4 (Me)]. Elemental analyses and mass spectroscopy indicated that 2 had the molecular formula [Mo2(MeC2Me)4-(ij5-C5H5)2] in agreement with the NMR data.…”

“…For our initial studies the protonation reaction was chosen. Treatment of 2 with an excess of anhydrous trifluoroacetic acid at 0 °C led to a rapid reaction and the formation of the purple crystalline salt [Mo2- (4), Mo(l)-C(3) = 2.317 (4), Mo(2)-C(4) = 2.240 (4), Mo(2)-C(5) = 2.287 (4), Mo(l)-C(6) = 2.341 (5), Mo(l)-C(7) = 2.321 (4), Mo-(1)-C(8) = 2.233 (4), C(l)-C(2) = 1.426 (5), C(2)-C(3) = 1.414 (6), C(3)-C(4) = 1.499 (5), C(4)-C(5) = 1.429 (7), C(5)-C(6) = 1.524 ( 6), C(6)-C(7) = 1.412 (6), C(7)-C(8) = 1.435 (7) A. 3 Hz), 7.87 (s, 3 H, Me), 7.96 (s, 3 H, Me), 9.03 (d, 3 H, Me, /hh = 2 Hz), 9.06 (s, 3 H, Me), 19.37 (m, 1 H, MoHC)].…”