Optically Active 4-Substituted 5-Nitropentan-2-ones: Valuable Chiral Building Blocks for the Stereocontrolled Construction of Spiro-Pyrazolone Scaffolds with Five Contiguous Stereogenic Centers

The application of readily available optically active 4-substituted 5-nitropentan-2-ones as chiral building blocks in the stereocontrolled construction of spiro-pyrazolone scaffolds was investigated. In the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (1 equiv.) optically active 4-substituted 5-nitropentan-4-ones exhibited excellent chiral inducing abilities in the diastereoselective cascade Michael/aldol reaction with a wide range of unsaturated pyrazolones to generate the corresponding biologically significant spiro-pyrazolone derivatives with five contiguous stereocenters in acceptable to good yield with high levels of diastereoselectivity.