Brønsted acid TfOH-mediated reactions of 2-(arylmethylene)cyclopropylcarbinols with acetonitrile

Rapid Access to Arylated and Allylated Cyclopropanes via Brønsted Acid-Catalyzed Dehydrative Coupling of Cyclopropylcarbinols

A regioselective protocol for the synthesis of cyclopropyl derivatives that relies on Brookhart acid-catalyzed dehydrative coupling over substituted cyclopropylcarbinols without rearrangement is reported herein. The reactions proceed promptly at 25 °C with only 2.0 mol % catalyst loading and produce the cyclopropyl derivatives in excellent yields. This method is well tolerated with a vast range of cyclopropylcarbinols including aliphatic cyclopropylcarbinols, where no elimination product was obtained, demonstrating the protocol's utility. Further, the Hammett correlation suggested the formation of a cyclopropylcarbinyl cation followed by a coupling reaction. An extremely effective gram-scale reaction has also been demonstrated with a high turnover number.

Intramolecular cyclopropylmethylation via non-classical carbocations

Cyclopropyl-cyclopropyl rearrangement can be achieved selectively by intramolecular trapping of cyclopropylmethyl carbenium ions with an internal nucleophile. This can be exploited as a useful method for the introduction of a cyclopropyl group into complex molecules using readily accessible disubstituted cyclopropane intermediates.

Brønsted Acid-Mediated Stereoselective Cascade Construction of Functionalized Tetrahydropyrans from 2-(Arylmethylene)cyclopropylcarbinols and Aldehydes

(E)- and (Z)-2-(Arylmethylene)cyclopropylcarbinols 1 could be converted to the corresponding tetrahydropyrans 2 and 3 stereoselectively in the presence of Brønsted acids MsOH or TsOH under mild conditions. A plausible Prins-type reaction mechanism has been proposed.