Abstract
Metal-free transformations of organotrifluoroborates are advantageous since they avoid the use of frequently expensive and sensitive transition metals. Lewis acid-catalyzed reactions involving potassium trifluoroborate salts have emerged as an alternative to metal-catalyzed protocols. However, the drawbacks to these methods are that they rely on the generation of unstable boron dihalide species, thereby resulting in low functional group tolerance. Recently, we discovered that in the presence of a Brønsted acid, trifluoroborate salts react rapidly with in situ generated oxocarbenium ions. Here, we report Brønsted acid-catalyzed direct substitution of 2-ethoxytetrahydrofuran using potassium trifluoroborate salts. The reaction occurs when tetrafluoroboric acid is used as a catalyst to afford functionalized furans in moderate to excellent yields. A variety of alkenyl- and alkynyltrifluoroborate salts readily participate in this transformation.
Highlights
Ethers are an important functional group in organic chemistry as they are present in pharmaceutical agents and bioactive compounds [1]
Our group has discovered that Brønsted acid-catalyzed reactions of benzhydryl alcohols [4] and acetals/ketals [5] with organotrifluoroborates proceed with excellent functional group tolerance
Synthesize trans‐α‐alkynyl‐β‐halo pyran furanusing derivatives is known [47]. and Lastly, Whilefunctionalization a range of methodologies exists for preparation of 2-alkenyl and 2-alkynyland tetrahydrofurans, of THF derivatives hasthe been achieved using organotrifluoroborates trityl ions the necessity to use stoichiometric amountsexists of a Lewis expensive catalysts and sensitive
Summary
Ethers are an important functional group in organic chemistry as they are present in pharmaceutical agents and bioactive compounds [1]. Alcohols have proven sulfimide to be suitable derivatives [35],the terminal alkynes alkynyl bromides [38,39], acid derivatives [40], and reagents towards synthesis of [36,37], the cyclic ether products, in cinnamic the presence of palladium ethynylbenziodoxolones [41] and β‐bromostyrenes [42]. Diastereoselective zinc-catalyzed alkynylation of α-bromo oxocarbenium reagents towards the synthesis of the cyclic ether products, in the presence of palladium and gold ions to synthesize trans-α-alkynyl-β-halo pyran and furan derivatives is known [47]. Whilefunctionalization a range of methodologies exists for preparation of 2-alkenyl and 2-alkynyland tetrahydrofurans, of THF derivatives hasthe been achieved using organotrifluoroborates trityl ions the necessity to use stoichiometric amountsexists of a Lewis expensive catalysts and sensitive [48].
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