Regioselectivities in Fe(III)‐catalyzed Cycloisomerization Reactions of γ‐Allenyl Alcohols

Abstract

Iron-catalyzed intramolecular hydroalkoxylation reactions of allenes were performed to provide various tetrahydrofurans by regioselective 5-exo cyclization pathway, as the Lewis acidic activation of Fe(III) salts toward unsaturated C C bonds, allenes and alkenes. Cyclohexyl substituted allenes especially isomerized to dienes at a rapid rate, which underwent a competing 6-endo cyclization mode. The plausible mechanism was presented by experimental results of the reaction intermediates and computational study of Fe-allene and Fe-diene complexes.

First-Row Late Transition Metals for Catalytic Alkene Hydrofunctionalisation: Recent Advances in C-N, C-O and C-P Bond Formation

“…More recently Kang et al, have shown that the temperature influences the isomerisation and the endo / exo -methylene selectivity of hydroalkoxylation products of cyclohexyl-substituted allene catalysed by iron(III) tosylate ( Scheme 10 ) [ 45 ]. At 50 °C, a partial isomerisation of allenol 1 in 2 occurs and during the catalytic process, 1 is converted into tetrahydrofuran 3 via a 5- exo -trig cyclisation.…”

Fe(II)/Fe(III)-Catalyzed Intramolecular Didehydro-Diels–Alder Reaction of Styrene-ynes

“…These available methods, however, need an additional functional group to accelerate reactivities of the Diels–Alder and consecutive reaction, and a more versatile approach was considered necessary. Inspired by our recent studies on Fe-catalyzed C–C multiple bond (allene and diene) activation, we envisaged that the relatively unactivated styrene-ynes could participate in didehydro-Diels–Alder reaction. Thus, polycyclic aromatic frameworks could be prepared using the π activation ability of the green and nontoxic iron catalysts.…”

Earth-Abundant 3d Transition Metal Catalysts for Hydroalkoxylation and Hydroamination of Unactivated Alkenes

“…This methodology is restricted to trialkylated allenols as mono-and dialkylated did not undergo cyclization under these conditions. The Fe(OTs)3 system can also be applied to the cyclization of -allenyl alcohols with concomitant alkene isomerization (Figure 3, top) [52]. During the reactivity study of -cyclohexyl-substituted allenic alcohols by this catalytic system, it was shown that the temperature influences not only the isomerization of the hydroalkoxylation products but also the endo/exo-methylene selectivity.…”