Regio- and Chemoselective Synthesis of 3-(Dihydrofuran-3(2)-ylidene)isobenzofuran-1(3)-imines Tandem Alkynyl Prins- and Intramolecular Oxycyclization Reactions.

A metal-free Lewis acid-initiated protocol for the synthesis of highly substituted 3-(dihydrofuran-3(2)-ylidene)isobenzofuran-1(3)-imines from 2-(4-hydroxybut-1-yn-1-yl)benzamides and aldehydes has been demonstrated. The reaction involves the initial formation of dihydrofuranylidene carbocation a Prins cyclization reaction using BF·OEt, followed by intramolecular cyclization to produce 3-(dihydrofuran-3(2)-ylidene)isobenzofuran-1(3)-imines up to / = 6:1 with moderate to good yields. The methodology can also be used for the synthesis of 3-(dihydro-2-pyran-3(4)-ylidene)-isobenzofuran-1(3)-imines. The strategy leads to the formation of two C-O bonds and one C-C bond with two different heterocycles connected by a tetra-substituted double bond. Post synthetic application of the reaction was extended for the synthesis of furanylidene isobenzofuranones in excellent yields.