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3.3.1.2.1 Enantioselective Reactions

DOI: 10.1055/sos-SD-203-00068

Shibata, T.Science of Synthesis: Stereoselective Synthesis, (20113127.

The rhodium-catalyzed carbonylative coupling of enynes with carbon monoxide using dicarbonylchlororhodium(I) dimer {[RhCl(CO)2]2} proceeds smoothly at atmospheric pressure. Although the addition of a phosphine ligand deactivates the rhodium catalyst,[‌10‌] the cationic rhodiumdiphosphine ligand complex, prepared by anion exchange using a silver salt, demonstrates high catalytic activity. This represents the first enantioselective PausonKhand reaction with a late-transition-metal complex using the axially chiral diphosphine ligand 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BINAP).[‌11‌] Unlike the chiral cyclopentadienyl ligand in the titanium complex described in Section 3.3.1.1, BINAP is commercially available and air stable, making this a practical alternative. The reaction was originally performed by heating the components at reflux in tetrahydrofuran under atmospheric pressure or a pressurized atmosphere of carbon monoxide. By this method, the yield and enantioselectivity are moderate to good depending on the substrate.[‌11‌] On the other hand, under a low partial pressure of carbon monoxide,[‌12‌] the reaction proceeds at ambient temperature with carbon- and heteroatom-tethered 1,6-enynes using 2,2-bis[bis(3,5-dimethylphenyl)phosphino]-1,1-binaphthyl (XylBINAP; 5) as a chiral ligand to provide the enantiomerically enriched bicyclopentenones 6 with excellent yield and enantioselectivity (Scheme 3).[‌13‌] Near-perfect enantioselectivity is achieved even with an enyne having an unsubstituted alkyne moiety.

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M 8-MeM8M8 8 88 88 [‌88‌]
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M(MM8Me)8 Me 8 88 88 [‌88‌]

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M M8 ee (%) Meeee (%) Mee
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MMe Me 88 88 [‌88‌]

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References


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