Spiro Fused Isoxazolines

Sasai s group [13] developed a series of bisnitrogen ligands with fused hetero spiro cyclic backbones, including spiro bis(isoxazoline) 11 and 12, spiro isoxazole-isoxazoline 13, spiro bis(oxazoline) 14, spiro bis(pyrazole) 15, and spiro bis(isoxazole) 16 (Figure 3). Ligands 11 [14] and 13 [15] exhibited excellent reactivity and enantioselectivity in the Pd-catalyzed oxidative cyclization reactions. 

Swem oxidation of isoxazolines 795 yields p-ketoesters 796 in moderate yields. By treatment with hydrazines, p-ketoesters 796 can be condensed to give the corresponding hydrazones 797, which concomitantly undergo elimination to give novel spiro-fused isoxazolinopyrazolones 798 (3,7,9-substituted-l-oxa-2,7,8-tri-azaspiro[4.4]nona-2,8-dien-6-one) in moderate to good yields (Scheme 4.231). ... 

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