We report herein a powerful and highly stereoselective protocol for the domino-type reaction of diazoesters with ortho-quinone methides generated in situ to furnish densely functionalized chromans with three contiguous stereogenic centers. A transition-metal and a Brønsted acid catalyst were shown to act synergistically to produce a transient oxonium ylide and ortho-quinone methide, respectively, in two distinct cycles. These intermediates underwent subsequent coupling in a conjugate-addition-hemiacetalization event in generally good yield with excellent diastereo- and enantioselectivity.
Keywords: ortho-quinone methides; oxonium ylides; phosphoric acids; rhodium; synergistic catalysis.
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