Tandem [1,5]-H shift/6π-electrocyclizations of ketenimines bearing 1,3-oxathiane units. Computational assessment of the experimental diastereoselection
摘要:
N-Aryl ketenimines bearing a 1,3-oxathiane function at the ortho position of the keteniminic nitrogen atom convert into spiro[1,3-oxathiane-2,4'(3'H)quinolines] under mild thermal treatment. These cyclization processes are interpreted in terms of a two-step tandem sequence involving a [1,5]-H migration followed by a 6 pi-electrocyclic ring closure. Moreover, the cyclization of 1,3-oxathiane-ketenimines having two different substituents at the terminal carbon atom of the ketenimine moiety provided spiroquinolines bearing two stereocenters, the C3 and C4 atoms, with moderate diastereoselectivity. A DFT study support that the mechanism of these conversions consists of a [1,5]-H shift/6 pi-electrocyclization sequence, in which the [1,5]-H shift is the rate-limiting step. A quantitative kinetic analysis of the cyclization of an oxathiane-ketenimine with a prochiral ketenimine function explains the sense and degree of the experimentally observed diastereoselectivity. (C) 2012 Elsevier Ltd. All rights reserved.
Tandem [1,5]-H shift/6π-electrocyclizations of ketenimines bearing 1,3-oxathiane units. Computational assessment of the experimental diastereoselection
摘要:
N-Aryl ketenimines bearing a 1,3-oxathiane function at the ortho position of the keteniminic nitrogen atom convert into spiro[1,3-oxathiane-2,4'(3'H)quinolines] under mild thermal treatment. These cyclization processes are interpreted in terms of a two-step tandem sequence involving a [1,5]-H migration followed by a 6 pi-electrocyclic ring closure. Moreover, the cyclization of 1,3-oxathiane-ketenimines having two different substituents at the terminal carbon atom of the ketenimine moiety provided spiroquinolines bearing two stereocenters, the C3 and C4 atoms, with moderate diastereoselectivity. A DFT study support that the mechanism of these conversions consists of a [1,5]-H shift/6 pi-electrocyclization sequence, in which the [1,5]-H shift is the rate-limiting step. A quantitative kinetic analysis of the cyclization of an oxathiane-ketenimine with a prochiral ketenimine function explains the sense and degree of the experimentally observed diastereoselectivity. (C) 2012 Elsevier Ltd. All rights reserved.
Tandem [1,5]-H shift/6π-electrocyclizations of ketenimines bearing 1,3-oxathiane units. Computational assessment of the experimental diastereoselection
N-Aryl ketenimines bearing a 1,3-oxathiane function at the ortho position of the keteniminic nitrogen atom convert into spiro[1,3-oxathiane-2,4'(3'H)quinolines] under mild thermal treatment. These cyclization processes are interpreted in terms of a two-step tandem sequence involving a [1,5]-H migration followed by a 6 pi-electrocyclic ring closure. Moreover, the cyclization of 1,3-oxathiane-ketenimines having two different substituents at the terminal carbon atom of the ketenimine moiety provided spiroquinolines bearing two stereocenters, the C3 and C4 atoms, with moderate diastereoselectivity. A DFT study support that the mechanism of these conversions consists of a [1,5]-H shift/6 pi-electrocyclization sequence, in which the [1,5]-H shift is the rate-limiting step. A quantitative kinetic analysis of the cyclization of an oxathiane-ketenimine with a prochiral ketenimine function explains the sense and degree of the experimentally observed diastereoselectivity. (C) 2012 Elsevier Ltd. All rights reserved.