Electrophilic Bromolactonization of Cyclopropyl Carboxylic Acids Using Lewis Basic Sulfide Catalyst

Abstract

Ah ighly facile and efficient electrophilic bromolactonization of cyclopropylcarboxylic acids could be effected by aL ewis basic sulfide catalyst. Mechanistic studies performed revealed that the cyclopropanes ubstrates could undergo radical bromination upon exposure to light, yielding am ixture of regioisomers.I ns tark contrast, the Lewis basic sulfide catalyst could promote the electrophilic bromolactonization and yield the Markovnikov product exclusively.

Applications of Selenonium Cations as Lewis Acids in Organocatalytic Reactions

“…In particular,t he cyclopropane system is known to readily react with electrophilic halogen sources to give ringopening species. [20] Nonetheless,t he reaction of 7h still gave the corresponding monobrominated product 8h (97 %) with the cyclopropane ring being intact. It is also worth mentioning that position-selective monobromination of these polycyclic arenes is not atrivial task and amixture of polyhalogeneated products are commonly observed when using conventional halogenation protocols.While there are several protocols that involve the use of metal catalysts or molecular bromine could effect the positional selective aromatic halogenation reactions, [21] the reaction system with 6 as the catalyst offers amild and metal-free alternative.…”

“…The performance of 6fis better than 6g,attributed to the fact that the relatively less coordinative tetrafluoroborate anion might enhance the Lewis acidity of the sulfonium center. [20] Nonetheless,t he reaction of 7h still gave the corresponding monobrominated product 8h (97 %) with the cyclopropane ring being intact. [11] 6b was used as the catalyst to evaluate other reactions.…”

Lewis Base‐Promoted Ring‐Opening 1,3‐Dioxygenation of Unactivated Cyclopropanes Using a Hypervalent Iodine Reagent

“…It is believed that the Lewis base‐activated halonium species could react with olefinic substrate to give the key intermediate haliranium ion followed by the ring‐opening of the haliranium ion by a nucleophile to give desired halogenated product . In a continuation of this endeavor, recently we applied the Lewis base catalytic protocol to the electrophilic halocyclization of cyclopropyl substrate and the haliranium ion‐like intermediate is believed to be involved in the reaction to give the ring‐opening/1,3‐difunctionalization product ,. Hypervalent iodine reagents (HIRs), for example phenyliodine bis(trifluoroacetate) (PIFA), are known to readily react with olefins to give the corresponding 1,2‐dioxygenated products and the reaction mechanism is similar to that of electrophilic halogenation .…”

“…In alignment with our research interest on Lewis base‐catalyzed reactions with olefinic and cyclopropyl substrates,, we hypothesized that a Lewis base promoter could react with HIR to in situ generate the positively charged species A , which could be a more active electrophile for the electrophilic ring‐opening/1,3‐difunctionalization of unactivated cyclopropanes 1 [Scheme , Eq. (3)] …”

Lewis Base Catalyzed Stereo‐ and Regioselective Bromocyclization

“…In parallel with our research campaign on electrophilic halogenation reactions using olefins, we also examined the possibility of using cyclopropane as the partner in halocyclization. Recently, we reported a Lewis base sulfide catalyzed electrophilic bromocyclization of cyclopropylmethyl carboxylic acid 131 , while Hennecke and Rösner reported bromocyclization of cyclopropane under catalyst‐free conditions . It is worth noting that cyclopropane contains three π‐character σ bonds.…”