Enantioselective Synthesis of Spiropyrazolone-Fused Cyclopenta[c]chromen-4-ones Bearing Five Contiguous Stereocenters
Pankaj V Khairnar1, Yin-Hsiang Su1, Athukuri Edukondalu1
1Department of Chemistry, National Taiwan Normal University, 88, Sec. 4, Tingchow Road, Taipei 11677, Taiwan R.O.C.
Abstract:
An enantioselective synthesis of spiropyrazolone-fused cyclopenta[c]chromen-4-ones is demonstrated via a (3+2) cycloaddition reaction. The reactions of 3-homoacylcoumarins and α,β-unsaturated pyrazolones in the presence of the cinchona-alkaloid derived hydrogen-bonding catalyst provide aforementioned spiropyrazolone-chromenone adducts bearing five contiguous stereocenters, of which one is the spiro all-carbon quaternary stereocenter in high yields (up to 98%) with good to excellent stereoselectivities (>25:1 dr and up to 99% ee). This one-pot methodology could also be practically demonstrated on a gram-scale with similar efficacy.
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