Oxidative Catalytic Spiroketalization Leading to Diastereoselective Synthesis of Spiro[benzofuran‐2,1′‐isochromene]s

Abstract

A new one-pot, two-step silver-catalyzed spiroketalization of the in-situ generated quinone imine ketals (QIKs) with b-alkynyl ketones has been established, enabling multiple CÀO and CÀC bond-forming reactions to access densely functionalized spiro[benzofuran-2,1'-isochromene] derivatives with generally good yields. The use of b-alkynyl ketones bearing alkyl and aryl groups located at the a-position of the carbonyl group could lead to highly diastereoselective spiro[chromane-2,1'-isochromene] derivatives. The reaction features broad substrate scope, mild oxidative catalytic conditions and excellent diastereoselectivity.

Bimetallic Catalytic Asymmetric Tandem Reaction of β‐Alkynyl Ketones to Synthesize 6,6‐Spiroketals

“…However, the vicinal C(sp 3 )−H bond functionalization of Int A was still challenging for the low reactivity. Recently, Jiang, Tu and co‐workers disclosed that β‐alkynyl ketones could also undergo an intramolecular oxo‐cyclization/H‐transfer sequence in the presence of silver salts, and generated the novel electron‐donating alkene Int ‐ B , which spiroketalized with quinone precursors at the site of the exocyclic double bond (Scheme a) ,. It could also be trapped by diarylphosphine oxide radicals, nitro radicals or N ‐fluorobenzenesulfonimide ,,.…”

An Overview of Ag‐catalyzed Synthesis of Six‐membered Heterocycles

“…Highly functionalized spiro[benzofuran‐2,1′‐isochromene] scaffolds 130 synthesis was achieved by a two‐step spiroketalisation catalyzed by AgTFA [76] . The substrates of the reaction were, β ‐alkynyl ketones 62 and N ‐(4‐hydroxyphenyl)sulfonamides 129 (Scheme 72).…”

Dual Palladium/Scandium Catalysis toward Rotationally Hindered C3‐Naphthylated Indoles from β‐Alkynyl Ketones and o‐Alkynyl Anilines

“…Over the past decade, the conjugated β‐alkynyl ketones, a class of activated internal alkynes, have demonstrated their powerful synthetic potential in an assortment of metal‐catalyzed annulation processes for the delivery of biologically important cyclic structures in a convergent manner. [ 28‐36 ] The pioneering works of Asao and Yamamoto have facilitated extensive studies on the metal‐catalyzed [4 + 2] cycloadditions of conjugated β‐alkynyl ketones with alkenes or alkyne for the synthesis of naphthalenes, in which the key is to generate in situ benzopyrylium intermediates as 1,4‐dipoles. [ 37‐38 ] Recently, we have established a series of silver‐catalyzed spiroketalization reactions of β‐alkynyl ketones…”