Enantioselective Synthesis of C₂-Symmetric Dimethyl Cyclohexadiene­dicarboxylates through Cationic Rhodium(I)/Modified-BINAP-Catalyzed [2+2+2] Cycloadditions

Abstract

A cationic rhodium(I)/(S)-Tol-BINAP complex was employed to catalyze an enantioselective intramolecular [2+2+2] cycloaddition of a trans enediyne leading to a C 2 -symmetric tricyclic dimethyl cyclohexadienedicarboxylate in 95% yield with 59% ee. A cationic rhodium(I)/(R)-H 8 -BINAP complex was employed to catalyze an intermolecular [2+2+2] cycloaddition of 1,6-diynes with dimethyl fumarate leading to C 2 -symmetric bicyclic dimethyl cyclohexadienedicarboxylates in 35-96% yields with ee values of 82-98%.

Alkenes in [2+2+2] Cycloadditions

“…[42] The asymmetric version of these totally intramolecular reactions appeared in 2007 when the catalytic system formed by ac ationic rhodium(I) complex with BINAP-type ligandscatalyzed enantioselective cycloadditionso fe nediynes resultingi n good yields and moderate enantiomeric excesses. [43] Shibata, using as imilar catalytic system, performed intramolecular cycloadditions of various carbon-, N-tosyl-,a nd oxygen-tethered enediynes, which gave the corresponding cyclohexa-1,3-dienes with high enantioselectivities (Scheme 20). [44] More recently, Nphosphino-tert-butylsulfinamide (PNSO) ligandsw ere used in rhodium(I)-catalyzed [2+ +2+ +2] cycloadditionr eactions of macrocyclic enediynes.…”

“…The stereochemistry of the olefinic moiety determined the final product configuration and thus E starting materials gave dl cycloadducts, whereas those with a Z olefin gave meso cycloadducts . The asymmetric version of these totally intramolecular reactions appeared in 2007 when the catalytic system formed by a cationic rhodium(I) complex with BINAP‐type ligands catalyzed enantioselective cycloadditions of enediynes resulting in good yields and moderate enantiomeric excesses . Shibata, using a similar catalytic system, performed intramolecular cycloadditions of various carbon‐, N ‐tosyl‐, and oxygen‐tethered enediynes, which gave the corresponding cyclohexa‐1,3‐dienes with high enantioselectivities (Scheme ) .…”

P‐Stereogenic Secondary Iminophosphorane Ligands and Their Rhodium(I) Complexes: Taking Advantage of NH/PH Tautomerism

“…Enediynes with terminal alkynes are challenging substrates to cyclize 18. For instance, Tanaka reported the Rh‐catalyzed cyclization of 17 with 78 % yield and 48 % ee using the tolbinap/[Rh(cod) 2 ]BF 4 system (tolbinap=2,2′‐bis[di( p ‐methylphenyl)phosphino]‐1,1′‐binaphthyl) 19. The PNSO ligands showed an acceptable reactivity profile, but afforded low selectivity (up to 32 % ee ).…”

P‐Stereogenic Secondary Iminophosphorane Ligands and Their Rhodium(I) Complexes: Taking Advantage of NH/PH Tautomerism

“…[17] Enediynes with terminal alkynes are challenging substrates to cyclize. [19] The PNSO ligands showed an acceptable reactivity profile, but afforded low selectivity (up to 32 % ee). [19] The PNSO ligands showed an acceptable reactivity profile, but afforded low selectivity (up to 32 % ee).…”

“…[18] For instance, Tanaka reported the Rh-catalyzed cyclization of 17 with 78 % yield and 48 % ee using the tolbinap/[Rh-(cod) 2 ]BF 4 system (tolbinap = 2,2'-bis[di(p-methylphenyl)phosphino]-1,1'-binaphthyl). [19] The PNSO ligands showed an acceptable reactivity profile, but afforded low selectivity (up to 32 % ee). The low selectivity was attributed to the fact that the chiral information in these ligands is located at the hemilabile sulfinyl group.…”