A Facile Synthesis of Cyclopenta[d][1,2]oxazines through [6+4] Cycloaddition Reaction

There have been only limited methods for the synthesis of cyclopenta[d][1,2]oxazines and their derivatives. Linn and Sharkey reported the first practical synthesis of cyclopenta[d][1,2]oxazine by use of benzoylated cyclopentadiene. Lloyd and co-workers also reported the synthesis of cyclopenta[d][1,2]oxazine by reaction of diaroylcyclopentadi-enes with hydroxylamine. The reaction of benzonitrile oxide with fulvene was known to yield both 1 : 1 and 2 : 1 adducts. Herein, we report the first example of a facile and convenient synthesis of various cyclopenta[d][1,2]oxazines starting from chlorooxime and fulvene through [6+4] cycloaddition. In an effort to pursue of PTP1B inhibitors, a convenient synthesis of functionalized cyclopenta[d][1,2]-oxazine derivatives was required. Fulvenes were obtained from the reaction of dimethyl sulfate salt of dimethylamides and cyclopentadienyl sodium as cited