Asymmetric Schmidt reaction of hydroxyalkyl azides with ketones.
An asymmetric equivalent of the Schmidt reaction permits stereocontrol in ring expansions of symmetrical cyclohexanones. The procedure involves the reaction of chiral 1,2- and 1,3-hydroxyalkyl azides with ketones under acid catalysis; the initial reaction affords an iminium ether that can be subsequently opened with base. A systematic study of this reaction is reported, in which ketone substrates, chiral hydroxyalkyl azides, and reaction conditions are varied. Selectivities as high as ca. 98:2 are possible for the synthesis of substituted caprolactams, with up to 1,7-stereoselection involved in the overall process. The fact that either possible migrating carbon is electronically identical provides an unusual opportunity to study a ring-expansion reaction controlled entirely by stereoelectronic factors. The mechanism of the reaction and the source of its stereoselectivity are also discussed.
Sahasrabudhe
Kiran
K
Department of Medicinal Chemistry, 1251 Wescoe Hall Drive, Malott Hall, Room 4070, University of Kansas, Lawrence, KS 66045-2506, USA.
Gracias
Vijaya
V
Furness
Kelly
K
Smith
Brenton T
BT
Katz
Christopher E
CE
Reddy
D Srinivasa
DS
Aubé
Jeffrey
J
D001386:Azides / Q000138:chemical synthesis / Q000737:chemistry*; D003512:Cyclohexanones / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D007769:Lactams / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D013237:Stereoisomerism
D001386:Azides; D003512:Cyclohexanones; D007659:Ketones; D007769:Lactams