Highly Enantioselective Construction of a Chiral Spirocyclic Structure by the [2 + 2 + 2] Cycloaddition of Diynes and exo‐Methylene Cyclic Compounds.

Abstract

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Catalytic Enantioselective Construction of Spiro Quaternary Carbon Stereocenters

“…For example, in 2006 Shibata and co-workers developed a Rh-catalyzed enantioselective [2 + 2 + 2] cycloaddition of diynes 111 and exo-methylene cyclic compounds 112 for the synthesis of quaternary spirocycles 114 (Scheme 28). 62 It was found that 5 mol % (S)-xylylBINAP 113 and Rh(cod)BF 4 complex turned out to be powerful catalysts for the transformation, which afforded a broad range of spirocyclic products 114 in good to excellent yields and enantioselectivities. In this cycloaddition, an oxidative coupling of diyne 111 first occurs to generate bicyclic metal-Scheme 28.…”

Catalytic Asymmetric Synthesis of Butenolides and Butyrolactones

“…In 2006, Shibata and Tsuchikama developed the Rh-catalyzed highly enantioselective cycloaddition between diynes and αmethylene-γ-butyrolactone (Scheme 132). 375 The mechanism of this reaction has been proposed as follows: an oxidative coupling gives a bicyclic metallacyclopentene, in which no asymmetric carbon atom is generated. The subsequent insertion of a 1,1disubstituted alkene along with reductive elimination affords a chiral quaternary carbon center in the ring.…”

“…The subsequent insertion of a 1,1disubstituted alkene along with reductive elimination affords a chiral quaternary carbon center in the ring. 375 The reaction of nitrogen-and oxygen-tethered dialkynes with α-methylene-γbutyrolactone gave the desired products 236b and 236c with excellent stereoinduction (97% ee, 97% ee). This cycloaddition of an unsymmetrical dialkyne, which possesses a methyl group and a phenyl group on the alkyne termini, provides access to a spirobutyrolactone 237d bearing a quaternary carbon stereocenter with excellent regio-and enantioselectivities (99% ee).…”