Cobalt borohydride derivative

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

The reduction of the C-a-nitro function of new nitro-S-thiodisaccharide was performed in the same fashion as described by us earlier (3) with sodium borohydride/cobalt chloride complex. For the purpose of purification and isolation, the corresponding amino derivatives were acetylated in situ and selectively deprotected to free amino derivatives at C-2 by employing Hanessian methodology 26) using triethyloxonium fluoroborate. 

Since utilization of the ketone carbonyl was now complete, its removal was implemented via an efficient three-step sequence involving reductive cleavage of the derived selenocarbonate with tris(trimethylsilyl)silane [12] under free radical conditions [13]. With the acquisition of 17 in this manner, the serviceability of the reagent produced by adding sodium borohydride to cobaltous chloride for chemoselective reduction of the nitrile group [14] was assessed. Indeed, treatment of 17 in this manner, followed directly by basification with potassium hydroxide in methanol, secured 18. In this step as well as in the subsequent progression to the N-methyl derivative 19, no epimerization was seen within ring A. 

Optically active cobalt(ii) complexes have been used as catalysts for the enan-tioselective borohydride reduction of aromatic ketones employing pre-modified borohydride. A DKR was observed for the reduction of a 2-ethoxycarbonyl-1-tetralone derivative using pre-modified borohydride arising from NaBH4, tetrahydrofurfuryl alcohol (THFA) and ethanol (Scheme 2.72). 

Other papers on thioxanthene derivatives deal with the methylation, on sulphur and sulphoxide-oxygen respectively, of thioxanthene and thio-xanthone sulphoxide, the Beckmann rearrangement of thioxanthone oxime, and the quantitative reduction of thioxanthene sulphoxide to thioxanthene with sodimn borohydride-cobalt chloride, a reagent which appears to be of fairly neral applicability. ... 

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