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

• Published in: Advanced synthesis & catalysis 2012-04, Vol.354 (6), p.1114-1128
• Main Authors: Chen, Jie, Ni, Shengjun, Ma, Shengming
• Format: Article
• Language: English
• Subjects: alkylation; Catalysis; Catalysts: preparations and properties; Chemistry; CO bond cleavage; Exact sciences and technology; furans; General and physical chemistry; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Kinetics and mechanisms; lactones; Organic chemistry; Preparations and properties; Reactivity and mechanisms; regioselectivity; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 1615-4150; 1615-4169
• DOI: 10.1002/adsc.201100337

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.