Abstract
The domino three-component coupling reaction of arynes with DMF and active methylenes or methines was studied as a highly efficient method for preparing heterocycles. Coumarin derivative 5 was formed when diethyl malonate (2) or α-bromomalonate (3) were used as a C2-unit. In contrast, dihydrobenzofurans 7a and 7b were obtained by using α-chloroenolates generated from α-chloromalonates 4a and 4b and Et2Zn. The benzofuran 15a could be obtained by using ethyl iodoacetate (14) as a C1-unit. The one-pot conversion of dihydrobenzofurans 7a, 7b and 8a into benzofurans 15a and 15b was also studied. The direct synthesis of benzofuran 15b was achieved by using the active methine 18 having ketone and ester groups.
Highlights
Synthetic strategies involving domino or cascade process offer the advantage of multiple carboncarbon and/or carbon-heteroatom bond formations in a single operation [1]
We describe in detail our approach to prepare coumarin, dihydrobenzofuran and benzofuran derivatives via the three-component coupling process starting from arynes generated from ortho-(trimethylsilyl)aryl triflates
We have designed a new approach involving two steps which are induced by the high reactivity related to the strain energy of aryne A and the four-membered intermeditate B (Scheme 1) [37]
Summary
Synthetic strategies involving domino or cascade process offer the advantage of multiple carboncarbon and/or carbon-heteroatom bond formations in a single operation [1]. The recent aryne-based chemistry has achieved some remarkable success in the transition metal-catalyzed reactions [2–10], the transition metal-free reactions and other transformations [11–21]. These advances have shown that the insertion of arynes into various element-element σ-bonds can be Molecules 2014, 19 achieved even under the transition metal-free conditions. We reported the efficient insertion into the C=O bond of formamides [32,33], which was successfully applied into the domino process trapping the transient intermediates with nucleophiles [34–36]. We describe in detail our approach to prepare coumarin, dihydrobenzofuran and benzofuran derivatives via the three-component coupling process starting from arynes generated from ortho-(trimethylsilyl)aryl triflates
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