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Stereoconvergent Generation of a Contrasteric syn-Bicyclopropylidene (=syn-Cyclopropylidenecyclopropane) by Stille-Like Coupling

2013-05-01
GÜNEY, MURAT
Essiz, Selcuk
DAŞTAN, Arif
Balcı, Metin
De Lucchi, Ottorino
ŞAHİN, Ertan
Fabris, Fabrizio
Stereoisomerically pure endo- and exo-7-halo-7-(trimethylstannyl)benzonorcar-3-enes (=endo- and exo-(1-halo-1a,2,7,7a-tetrahydro-1H-cyclopropa[b]naphthalen-1-yl)trimethylstannane) 4 and 6 were selectively obtained by lithiumtin or magnesiumtin transmetalation in good yields (Scheme2 and 3). The reaction of these compounds with copper(I) thiophene-2-carboxylate (CuTC) produced in both cases the corresponding CS-symmetric bicyclopropylidene (=cyclopropylidenecyclopropane) syn-1, a single diastereoisomer (Schemes5 and 6). The structure of syn-1 was undoubtedly elucidated by X-ray single crystal diffraction. The coupling mechanism of the carbenoid cyclopropane is discussed (Scheme7).