Diastereo-differentiating intramolecular cyclopropanations of prochiral olefins and a diazo ester linked by optically active 2,4-pentanediol
Intramolecular cyclopropanation of 3, the substrate having a chiral auxiliary as a linking bridge between a diazo ester and cyclohexene, was found to give the cyclopropane 4 having over 99% diastereomeric excess (d.e.) in 91.5% yield. The reaction was als
Chiral and flexible 2,4-pentanediol-tethered cyclopropanation of olefins with a carbenoid derived from a diazo ester to construct three stereogenic centers
2,4-Pentanediol-tethered cyclopropanation of an olefin with an internal carbenoid generated from a diazo ester proceeded smoothly to give a chiral adduct having three stereogenic centers under full stereocontrol. The high stereoselectivity was not affected by the structure of the olefinic portion, studied so far with six substrates. Conversion of the product cyclopropane to other optically active compounds is also reported.
Temperature-independent stereocontrolled [2+2] cycloaddition. Potential of the 2,4-pentanediol tether in asymmetric reactions as a differential activation entropy promoter