Rhodium-catalyzed carbometalation of ynamides with organoboron reagents

Catalytic Asymmetric Dihydroxylation of Enamides and Application to the Total Synthesis of (+)‐Tanikolide

“…[18] The enamide employed in the initial part of this study are shown in Table 1, and were prepared according to one of the rhodium-catalyzed ynamide carbometalation procedures we have described recently. [14] The enamides 6 a, 6 b, and 6 d-6 g have been reported previously, [14] whereas enamides 6 c, 6 h, and 6 i are new compounds. [19] Highly enantioselective dihydroxylation of these substrates was readily accomplished using commercially available AD-mix-b without the addition of MeSO 2 NH 2 .…”

“…Our research group has recently developed rhodiumcatalyzed carbometalation reactions that offer solutions to many of these drawbacks. [14] Instead of providing enol derivatives 3, these reactions furnish b,b'-disubstituted enamides 6 [15] from the corresponding ynamides 5 [16] (Scheme 2). Collectively, these processes enable the introduction of alkyl, alkenyl, aryl, heteroaryl, benzyl, and alkynyl groups, and the presence of sensitive functional groups such as esters [14a-c] and ketones [14c] on the organometallic reagent is permitted.…”

Carbometallation Reactions

“…This Rh-catalyzed reaction was logically extended to the regioselective carbometallation of the same ynamide substrates with organoboron reagents [112]. In the presence of a substoichiometric amount of the [Rh(cod)(MeCN) 2 ]BF 4 complex, ynamides in aqueous THF under microwave irradiation underwent highly regioselective addition of organoboronic acids to the carbon-carbon triple bond (Scheme 10.133).…”

“…The authors proposed a catalytic cycle [112] the starting Rh complex is hydrolyzed, first to form a catalytically active Rh(I) hydroxide species 393.…”

“…Scheme 10.133Microwave-assisted rhodium-catalyzed carbometallation of ynamides with arylboronic acids[112].Scheme 10.134Possible catalytic cycle for the rhodium-catalyzed carbometallation with arylboronic acids[112].formed arylrhodium intermediate of type 394 to the carbon-carbon triple bond and the double bond of methyl acrylate (Scheme 10.136).…”