Tuning of Regioselectivity in Inorganic Iodide‐Catalyzed Alkylation of 2‐Methoxyfurans via Electronic and Steric Effects

Abstract

In the presence of inorganic iodide, the methoxy CO bond in 2‐methoxyfurans may be cleaved to afford the corresponding lactonic anion. Due to the presence of an electron‐withdrawing group at the 3‐position, the alkylation with normal organic iodides occurred at the 3‐position highly regioselectively. However, when electron‐deficient allylic iodides with an electron‐withdrawing group at the 2‐position were used the 5‐alkylation products were formed as the major products with sodium iodide as the catalyst. With magnesium iodide as the catalyst, the 5‐allylation occurred highly regioselectively. As a whole, the 3‐ vs. 5‐alkylation selectivity may be determined by the relative steric hindrance at the 3‐ and 5‐positions and the electronic effect of the allylic iodides. A rationale was proposed.

Selective Syntheses of Δα,β and Δβ,γ Butenolides from Allylic Cyclopropenecarboxylates via Tandem Ring Expansion/[3,3]-Sigmatropic Rearrangements

“…14 Recently, Ma described iodide catalyzed, regioselective alkylation of 2-methoxyfuran-3-carboxylic esters to give Δ α,β and Δ β,γ butenolides. 15 …”

Mechanistic Divergence in the Hydrogenative Synthesis of Furans and Butenolides: Ruthenium Carbenes Formed by gem‐Hydrogenation or through Carbophilic Activation of Alkynes

“…[8] Alternatively, 2 can be alkylated with allyl iodide to give product 4. [9] In other cases such as 5-7,t he furan itself was sufficiently stable for isolation. In line with our previous investigations, [2][3][4] different propargylic substituents (for example,-OR, -OSiR 3 , -OMOM) were found to instigate gem-hydrogenation.…”

Efficient Synthesis of Arylated Furans by a Sequential Rh‐Catalyzed Arylation and Cycloisomerization of Cyclopropenes

“…Cyclopropenes with different substituents (R 2 )such as cyclopentyl and cyclopropyl groups were also amenable to this transformation, giving the corresponding products in 80 %y ields (3n and 3o). [13,14] Based on the unique and diverse reactivities of cyclopropene, [6] we proposed four possible mechanistic pathways (Scheme 4; for details,see the Supporting Information). However,a nu nsubstituted cyclopropene dicarboxylate substrate did not show reactivity in this reaction.…”

“…Moreover,u sing ac atalytic amount of NaI, the reaction of 3q with 3iodopropene proceeded smoothly to afford the butenolide derivative 5. [13,14] Based on the unique and diverse reactivities of cyclopropene, [6] we proposed four possible mechanistic pathways (Scheme 4; for details,see the Supporting Information). Path (I) is asequential Rh-catalyzed isomerization of cyclopropene into afuran Rh species, [9] followed by the coupling with 1a.In path (II), an intermediate C is proposed to be formed from the coupling and ring-opening of the three-membered ring.…”