Synthesis and crystal structure of new dinitro derivatives of sesquiterpene lactone achillin

An unexpected dinitro derivative (2) of sesquiterpene lactone achillin (1), isolated from the aerial part of Achillea micrantha Wild., was formed when this compound was exposed to gaseous NOCl in CHCl3. This derivative was transformed into dinitrocarbonic acid (3) in pyridine in 30 minutes and in quantitative yield. The structures of these compounds were unambiguously determined by single-crystal X-Ray diffraction analysis.