204. New Ethylzinc Reagents with Remarkable Properties in palladium-catalyzed zinc-ene reactions
     Oppolzer, W.; Schröder, F.; Kahl, S.
     Helv. Chim. Acta 1997, 80, 2047-2057

Pd-Catalyzed Zn-ene allylic olefinations with the new ethylzinc reagents Et—Zn—OSO₂CF₃ (4) and Et—Zn—OC(O)CF(MeO)CF₃ (5) in CH₂Cl₂ showed an unexpected trans-selectivity in the ring closure to cyclopentane derivatives (see Scheme 2 and Table 1). This strongtrans-selectivity is in contrast with the corresponding known Zn-ene reaction using Et₂Zn in Et₂O which shows a high cis-selectivity (Table 1). The probable radical origin of the observed trans-selectivity is discussed. The Zn-ene reaction products of the type RZnOSO₂CF₃could be derivatized by the known protonation, iodination, and cyanation yielding 8–10 (Scheme 4 and Table 2), these derivatizations could furthermore be extended by allylation and oxidation reaction (→ 13, 15, and 16; see Scheme 5).

DOI : 10.1002/hlca.19970800705 

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