Regiodivergent Ligand-Controlled Rhodium-Catalyzed [(2+2)+2] Carbocyclization Reactions with Alkyl Substituted Methyl Propiolates

Enantioselective Construction of Tetrahydroindole Skeletons by Rh-Catalyzed [2+2+2] Cycloaddition of Homopropargyl Enamides with Alkynes

We have developed the Rh-catalyzed enantioselective [2+2+2] cycloaddition of homopropargyl enamides (tosylamide-tethered 1,6-enynes) with alkynes to construct tetrahydroindole skeletons found in natural alkaloids and pharmaceuticals. This cycloaddition proceeds at room temperature in high yields and regio- and enantioselectivity with a broad substrate scope. The preparative scale reaction followed by substituent conversion on the nitrogen atom and the diastereoselective [4+2] cycloaddition with singlet O2 affords hexahydroindole-diols bearing three stereogenic centers and variable substituents on the nitrogen. Mechanistic studies have revealed that the substituents of the enynes change the ratio of intramolecular and intermolecular rhodacycle formation when using terminal alkynes, varying the ee values of the cycloadducts.

Ligand-Controlled Copper-Catalyzed Regiodivergent Carbonylative Synthesis of α-Amino Ketones and α-Boryl Amides from Imines and Alkyl Iodides

Regioselective transformation is among the long-standing challenges in organic synthesis. In this communication, a copper-catalyzed selectivity controlled regiodivergent borocarbonylation of imines with alkyl iodides has been developed. Various α-amino ketones and α-boryl amides were produced in moderate to good yields from the same substrates. The choice of the ligand is key for the regioselectivity control: α-amino ketones were produced selectively in good yields with (p-CF₃ C₆ H₄ )₃ P as the ligand, whereas the corresponding α-boryl amides were obtained with high regioselectivities when using ^Me IMes as the ligand.

Ruthenium-Catalyzed [2+2+2] Cycloaddition of 1,6-Enynes and Unactivated Alkynes: Access to Ring-Fused Cyclohexadienes

The [2+2+2] intermolecular carbocyclization reactions between 1,6-enynes and alkynes catalyzed by [RuCl(cod)(Cp*)] (cod=1,5-cyclooctadiene, Cp*=pentamethylcyclopentadienyl) are reported to provide bicyclohexa-1,3-dienes. The presented reaction conditions are compatible with internal and terminal alkynes and the chemo- and regioselectivity issues are controlled by the presence of substituents at the propargyl carbon center of the alkyne(s) partner(s).

Enantioselective Rhodium-Catalyzed Cycloisomerization of (E)-1,6-Enynes

An enantioselective rhodium(I)-catalyzed cycloisomerization reaction of challenging (E)-1,6-enynes is reported. This novel process enables (E)-1,6-enynes with a wide range of functionalities, including nitrogen-, oxygen-, and carbon-tethered (E)-1,6-enynes, to undergo cycloisomerization with excellent enantioselectivity, in a high-yielding and operationally simple manner. Moreover, this Rh(I) -diphosphane catalytic system also exhibited superior reactivity and enantioselectivity for (Z)-1,6-enynes. A rationale for the striking reactivity difference between (E)- and (Z)-1,6-enynes using Rh(I) -BINAP and Rh(I) -TangPhos is outlined using DFT studies to provide the necessary insight for the design of new catalyst systems and the application to synthesis.

Rhodium-catalyzed regio-, diastereo-, and enantioselective [2+2+2] cycloaddition of 1,6-enynes with acrylamides

Ring ring: annulated cyclohexenes were synthesized by using the title reaction with the cationic rhodium(I)/(R)-H(8) -binap complex as a catalyst. In this catalysis, regioselective insertion of the acrylamide into a rhodacyclopentene intermediate and the coordination of the carbonyl group of the acrylamide to the cationic rhodium center suppress the undesired β-hydride elimination.