Cyclopropane derivativesQ 0021 DOI: 10.1002/chin.201151044

Highly Enantioselective Cyclopropenation Reaction of 1-Alkynes with α-Alkyl-−α-diazoesters Catalyzed by Dirhodium(II) Carboxylates. — Tetrabromophthalo-yl-protected tert-leucine represents an efficient ligand for the Rh-catalyzed asymmetric cyclopropenation of α-alkyl-α-diazoacetates with terminal alkynes. The cyclopropene-carboxylates containing an all-carbon quaternary stereocenter are formed in high yields and high to excellent enantioselectivities (up to 99% e.e.). Main side reaction is the al-kene formation by 1,2-hydride shift [cf. (IX)]. — (GOTO, T.; TAKEDA, K.; SHIMADA, N.; NAMBU, H.; ANADA, M.; SHIRO, M.; ANDO, K.; HASHIMOTO*, S.; Angew. Chem., Int. Ed. 50 (2011) 30, 6803-6808, http://dx.doi.org/10.1002/anie.201101905 ; Fac. Pharm. Sci., Hokkaido Univ., Sapporo 060, Japan; Eng.) — Mischke

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