New ethylzinc reagents with remarkable properties in palladium-catalyzed zinc-ene reactions

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 strong trans-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 R-Zn-OSO2CF3 could 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).