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

Abstract

Abstract Pd‐Catalyzed Zn‐ene allylic olefinations with the new ethylzinc reagents EtZnOSO 2 CF 3 ( 4 ) and EtZnOC(O)CF(MeO)CF 3 ( 5 ) in CH 2 Cl 2 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 Et 2 Zn in Et 2 O 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OSO 2 CF 3 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 ).