Iron-Catalyzed Ring Opening of Cyclopropanols and Their 1,6-Conjugate Addition to p-Quinone Methides

Abstract

A novel iron-catalyzed ring opening of cyclopropanols and their 1,6-conjugate addition to p-quinone methides for accessing substituted phenols is disclosed. In this protocol, various cyclopropanols are converted to alkyl radicals and undergo 1,6-conjugate addition to p-quinone methides toward C–C bond formation. The salient features of this methodology include operationally simple and mild reaction conditions, environmentally benign protocol, high efficiency, inexpensive catalyst, good to excellent yield, and a wide range of substrate scope.

Ring‐Opening Coupling Reaction of Cyclopropanols with Electrophilic Alkenes Enabled by Decatungstate as Photoredox Catalyst

“…The latter process is challenging due to the relatively strong OÀ H bond (typical BDE values 103-105 kcal mol À 1 ). [4] The traditional methods for the generation of radicals A with the subsequent addition to double bonds of olefins require strong oxidative conditions provided by stoichiometric oxidants [5] and/or transition metal derivatives (Ag(I), [6][7][8] Fe(III), [9][10][11] Mn(III) [12][13][14] ) and elevated temperatures. [5,6,10,11,14] Currently, photoredox catalysis offers a number of bypassing strategies that allow the generation of ketoalkyl radicals from cyclopropanols [15,16] and even unstrained cycloalkanols under mild conditions.…”

“…The latter process is challenging due to the relatively strong O−H bond (typical BDE values 103–105 kcal mol −1 ) [4] . The traditional methods for the generation of radicals A with the subsequent addition to double bonds of olefins require strong oxidative conditions provided by stoichiometric oxidants [5] and/or transition metal derivatives (Ag(I), [6–8] Fe(III), [9–11] Mn(III) [12–14] ) and elevated temperatures [5,6,10,11,14] …”

Metal-Free Approach for Oxa-spirocyclohexadienones through [3 + 2]/[4 + 2] ipso-Cyclization of para-Quinone Methides with Halo Alcohols

“…To overcome these challenges, our group recently demonstrated 1,6-conjugate addition of bis nucleophilic diols on p-QMs to get 1,4-dioxaspiro [5.5]undeca-7,10-diene-9-one under metal-free reaction conditions (Scheme 1d). 8f In continuation of our ongoing interest 9 first example of a highly robust and structurally interesting dearomative [3 + 2] and [4 + 2] ipso-cyclization/annulation of p-QMs with halohydrins chlorohydrin, bromohydrin, and iodohydrin and their homologues under basic conditions in high efficiency (Scheme 1e).…”

Ring-Opening Cross-Coupling of Cyclopropanols with Electrophilic Alkenes via Photoinduced Charge Transfer Facilitated by Decatungstate Catalyst

“…[35] In the work of Melchiorre et al, enantioselective photochemical cascade reaction of cyclopropanols and α,βunsaturated aldehydes was developed, which combined the excited-state and ground-state reactivity of chiral organocatalytic intermediates. [36] Traditionally, in similar non-photochemical reactions, transition metal derivatives (Ag(I), [37,38] Fe(III), [39][40][41] and Mn(III) [42][43][44] ) have been applied as catalysts, often in combination with additional oxidative reagents and under harsh reaction conditions. Moreover, stoichiometric oxidants can be used on their own, [45] without any catalytic assistance.…”