Sodium pentalene derivatives

The fermentation broth of various Streptomyces species can be separated into an acidic fraction shown to contain pentalenic acid 776) The somewhat less oxidized pentalenolactone precursor has been independently prepared from humulene from which is is probably derived biogenetically Thus, treatment of humulene with mercuric nitrate followed by aqueous potassium bromide solution gave two bromo-mercury derivatives which were oxygenated in the presence of sodium borohydride. The resulting pair of diols (770 and 771) were separately converted to exo methylene... 

The dark blue crystalline l,3-bis(dimethylamino)pentalene (157) was the second derivative to yield to synthesis (Scheme 26).233-1 Upon condensation of sodium cyclopentadienide with the salt 153, there is obtained the fulvene 154 which can be cyclized with loss of dimethylamine when heated in xylene. Treatment of the resulting ketone (155) with dimethylammonium perchlorate afforded the salt 156 which was successfully deprotonated with isopropylmagnesium bromide. Interestingly, 155 could be reversibly converted to its blue-colored enolate without polymerization or decomposition. 

Derivatives of the 2,5-diaza-l,6-dioxa-6a-selena(Se )pentalene (240) and l,2,5,6-tetraaza-6a-selena(Se )pentalene (241) systems were obtained through the oxidation of )S-diketone dioximes and diphenylhydrazones, respectively, with selenium dioxide. Another selena(Se )pentalene type (243) has been synthesized by treatment of the diselenolium salts 242 with sodium nitrite in acetic acid-acetonitrile. 

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