4-chloro-7-nitrobenzofurazan as a Diels-Alder reagent. A facile access to highly functionalized naphthofurazans

4-Chloro-7-nitrobenzo-2-oxa-1,3-diazole (4-chloro-7-nitrobenzofurazan or NB D chloride) is found to react instantaneously and quantitatively with trans -1-methoxy-3-(trimethylsilyloxy)-1,3-butadiene (Danishefsky's diene), to fo rm regioselectively the silyl enol ether 4, according to a normal electron- demand Diels-Alder (NEDDA) reaction. This provides the first evidence that this strongly electrophilic heterocycle can also exhibit pericyclic reactiv ity. Unmasking the enol 4 followed by treatment in the presence of 2 equiv. of base (DBN) leads to 4-chloro-7-hydroxynaphtho[1,2-c]furazan 7. We are t hus reporting an easy access to a functionalized hydroxynaphthofurazan, whi ch is obtained under mild conditions in three steps with greater than 80% o verall yield. (C) 2001 Elsevier Science Ltd. All rights reserved.