CHIRALITY TRANSFER IN 5-EXO CYCLIZATIONS OF AXIALLY CHIRAL O-IODOANILIDES

Stereoselective 5-exo radical and Heck cyclizations of axially chiral o-iodoanilides to enantioenriched oxindoles and dihydroindolones are described. Mechanisms for the transfer of chirality from the atropisomeric anilides to the newly formed stereocenters in the cyclic products are proposed and supported with physical data. Additionally, the N-aryl bond rotation barriers for eight o-iodoanilides are reported. A series of axially chiral N-allyl-o-iodoanilides were cyclized under room temperature radical conditions to dihydroindolones with good to excellent chirality transfer (74-97 %). Cyclization rate constant data is presented to rationalize the regioselective preference for N-allyl over N-acryloyl cyclization when an o-methyl group is present. X-ray crystallography was used to assign absolute configurations to a cyclization precursor/product pair. Radical 5-exo cyclizations of axially chiral o-iodoanilides bearing branched, bulky N-substituents are covered. The bulkiness of N-substituents permitted the resolution of a series of novel o-iodoanilides lacking a second ortho substituent. Radical cyclizations of these o-iodoanilides transferred this transient axial chirality into a new stereocenter in the oxindole products with high fidelity (78-92 %). The first Heck cyclizations of axially chiral o-iodoanilides with chirality transfer (84-89 %) are described. X-ray crystallographic data is presented for one anilide cyclization precursor with studies to elucidate the mechanism of chiral transfer.