Rhodium‐Catalyzed Regio‐, Diastereo‐, and Enantioselective [2+2+2] Cycloaddition of 1,6‐Enynes with Acrylamides

Abstract

Scheme 1. Transition-metal-catalyzed asymmetric [2+2+2] cycloadditions involving alkene units.

Catalytic Version of Enediyne Cobalt‐Mediated Cycloaddition and Selective Access to Unusual Bicyclic Trienes

“…But the major disadvantage for all those [Co(Cp)(L) 2 ] complexes is that in most cases a stoichiometric amount of cobalt is required due to the tendency for Co I or Co 0 to coordinate the final diene to form a very stable h 4 -(1,3-cyclohexadiene) and, therefore, block the catalytic cycle. For these reasons, other catalytic systems based on rhodium, iridium, or ruthenium are becoming more attractive for the enediyne cycloaddition [4] albeit using catalyst loadings up to 20 mol %. As an alternative to [Co(Cp)(L) 2 ] catalysts, we recently demonstrated that simpler and easier to handle systems consisting of [a] S.…”

“…Then, by simply mixing [CoA C H T U N G T R E N N U N G (acac) 2 ] (acac = acetylacetonate) with trimethylphosphine and sodium borohydride in THF, we were able to isolate the desired complex in 44 % yield on a two gram scale (Scheme 1). 4 ] was first evaluated with the well-known [2+2+2] cycloaddition of triynes. The reaction of different triynes 1 with variable tethers was conducted at room temperature in the presence of a catalytic amount of [Co(H)- 4 ].…”

“…4 ] was first evaluated with the well-known [2+2+2] cycloaddition of triynes. The reaction of different triynes 1 with variable tethers was conducted at room temperature in the presence of a catalytic amount of [Co(H)- 4 ]. As shown in Table 1, the catalyst is very efficient at low loadings (5 mol %) and except with a gem-diester tether ( Table 1, entry 4) the desired polycyclic aromatic systems 2 were obtained in good yields (65-70 %).…”

Rhodium‐Catalyzed Asymmetric [2+2+2] Cycloaddition of 1,6‐Enynes with Racemic Secondary Allylic Alcohols through Kinetic Resolution

“…[2] For example, our research group reported that ac ationic rhodium(I)/H 8 -binap complex is capableo fc atalyzing the regio-, diastereo-,a nd enantioselective [2+ +2+ +2] cycloaddition of 1,6-enynes [3,4] with acrylamides [5] giving chiral bicyclic cyclohexenes,p ossessing two stereogenic centers (Scheme 1a). [6] Not only acrylamides but also enamides [5a, 7] and oxabenzonorborna-dienes [8] could be employed in the rhodium-catalyzed asymmetric[ 2 + +2+ +2] cycloadditionw ith 1,6-enynes. In the reactions using acrylamides and enamides, the coordination of the amide carbonyl into rhodium induce high reactivity and selectivity,a nd suppresst he undesired b-hydrogen elimination giving dienep roducts.…”

Asymmetric Synthesis of Protected Cyclohexenylamines and Cyclohexenols by Rhodium‐Catalyzed [2+2+2] Cycloaddition

“…[3] In 2005, the groups of Evans and Shibata independently reported the rhodium(I)catalyzed enantioselective [2+ +2+ +2] cycloaddition of 1,6enynes with alkynes. [5][6][7][8][9] We anticipated that if high reactivity and selectivity of the reactions using acrylamides arise not from their electron-deficient nature but high coordination ability, highly coordinative electron-rich enamides [10] would also be suitable cycloaddition partners toward 1,6-enynes.Herein, we disclose the cationic rhodium(I) complex catalyzed regio-, diastereo-, and enantioselective [2+ +2+ +2] cycloaddition of 1,6enynes (1)with enamides and vinyl carboxylates (2). [5][6][7][8][9] We anticipated that if high reactivity and selectivity of the reactions using acrylamides arise not from their electron-deficient nature but high coordination ability, highly coordinative electron-rich enamides [10] would also be suitable cycloaddition partners toward 1,6-enynes.Herein, we disclose the cationic rhodium(I) complex catalyzed regio-, diastereo-, and enantioselective [2+ +2+ +2] cycloaddition of 1,6enynes (1)with enamides and vinyl carboxylates (2).…”