Molecular Sieve (MS 4A) Promoted Cyclocondensation of Hindered, Aromatic Nitrile Oxides and Cyclic Diketones under Mild Conditions

Abstract

Molecular sieves (MS 4A) serve as efficient promoters for the cyclocondensation of stable, hindered nitrile oxides and a variety of cyclic diketones to afford fused isoxazoles in good yield. The operational simplicity and remarkably mild reaction conditions compliment our amine-promoted cyclocondensation conditions and demonstrate broad substrate scope.

Key words

cycloadditions - ketones - condensation - isoxazoles - molecular sieves

References

• 1a Bode JW. Hachisu Y. Matsuura T. Suzuki K. Tetrahedron Lett.  2003,  44:  3555 
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• 2 For a review of molecular sieve and zeolite promoted reactions, see: Sen SE. Smith SM. Sullivan KA. Tetrahedron  1999,  55:  12657 
• 3 The use of 4 Å MS as a base for the elimination of C-chloroximes to form nitrile oxides and subsequent cycloaddition with acrylates has been reported. However, under these conditions long reaction times (7-10 d) were necessary, see: Kim JN. Ryu EK. Heterocycles  1990,  31:  1693 
• 5 Thermal cycloadditions of 2-hydroxynaphthoquinone and nitrile oxides have been previously reported: Brahmeshwari G. Rao VR. Rao TVP. Indian J. Chem., Sect. B  1995,  34:  139 
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• 9 For a Diels-Alder type cycloaddition reaction promoted by molecular sieves, see: Pindur U. Haber M. Heterocycles  1991,  32:  1463 

4

MS 4A have the general formula Na₂O·Al₂O₃·xSiO₂·yH₂O.