Mechanistic Study of the Rhodium‐Catalyzed [3+2+2] Carbocyclization of Alkenylidenecyclopropanes with Alkynes. Issue 9 (19th June 2013)

• Record Type: Journal Article
• Authors: Yu, Haizhu; Lu, Qianqian; Dang, Zhimin; Fu, Yao
• Is Part Of: Chemistry, an Asian journal. Volume 8:Issue 9(2013:Sep.)
• Page Start: 2262
• Page End: 2273
• Publication Date: 2013-06-19
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201300575
• Languages: English
• ISSNs: 1861-4728

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>A systematic theoretical study has been performed on the recently reported Rh<sup>I</sup>‐catalyzed [3+2+2] <named-content id="d408e1152" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">carbocyclization reactions</named-content> between alkenylidenecyclopropanes (ACPs) and alkynes. With the aid of theoretical calculations, two possible mechanisms, that is, alkene‐carbometalation‐first and alkyne‐carbometalation‐first mechanisms, are examined in this study. In the <named-content id="d408e1155" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">oxidative addition</named-content> step, the possibility of reaction on either the distal or proximal CC bond of the cyclopropane group has been evaluated. The calculations indicate that the alkene‐activation‐first mechanism is more favored for the overall catalytic cycle. This mechanism involves four steps, that is, <named-content id="d408e1158" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">oxidative addition</named-content> of the distal (rather than the proximal) CC bond of cyclopropane group, alkene <named-content id="d408e1161" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">carbometalation</named-content>, alkyne <named-content id="d408e1165" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">carbometalation</named-content>, and reductive elimination. The rate‐determining step in the overall catalytic cycle is the <named-content id="d408e1168" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">carbometalation</named-content> of the alkyne (i.e., the alkyne‐insertion step) and this step also determines the regioselectivity. Finally, the origin of the regioselectivity is determined by the steric effect (i.e., the steric crowding between the electron‐withdrawing group on alkyne and other ligands on the rhodium center) in the alkyne‐insertion step.</p> </abstract>