Reactions of 2-hydroxyaryl-α,β-unsaturated ketones with dimethylsulfonium carbonylmethylides: a new and facile diastereoselective synthesis of 2,3-disubstituted dihydrobenzofurans

Non-covalent interactions in the diastereoselective synthesis of cis-2,3-dihydrobenzofurans: experimental and computational studies

“…11 However, the reported cis stereochemistry could have been misinterpreted and under those conditions, the reaction yielded trans isomers, which is in agreement with the reported 1 H-NMR data of those products. 12 Interestingly, a similar strategy was reported in 2019 but this time in the vinylogous Michael addition of ortho -hydroxycinnamates, alkylated in situ with γ-bromocrotonate. 13 Nevertheless, using K 2 CO 3 and DMF or NMP as a solvent, the reaction afforded only 2,3-benzofurans whereas the corresponding 2,3-DHBs were not observed.…”

Formal [4+1] Annulation Reactions in the Synthesis of Carbocyclic and Heterocyclic Systems

“…In 2013, Xiao’s group achieved an enantioselective formal [4+1] annulation of salicyl aldimines 343 with camphor-derived sulfonium salts 344 , which facilitated the synthesis of trans -2,3-dihydrobenzofurans 345 in moderate to excellent yields (29–78%) with reasonable diastereo- and enantioselectivities (>95/5 dr, 21–98% ee) (Scheme ) . Modification of the reaction parameters, such as high temperature and microwave irradiation, has also been utilized to change the kinetic preference for the transformations of the sulfur ylides to synthesize 2,3-disubstituted dihydrobenzofuran derivatives . Analogous to the sulfur ylides, the 2-halo-1,3-dicarbonyl compounds can also undergo a formal [4+1] annulation with salicylic aldehyde derivatives, such as the 2-hydroxyaryl-α,β-unsaturated ketones, 2-hydroxyarylnitroalkenes, and 2-hydroxyarylimines, with K 2 CO 3 as the base, to produce a range of highly functionalized 2,3-dihydrobenzofurans with moderate to excellent yields …”

“…238 Modification of the reaction parameters, such as high temperature and microwave irradiation, has also been utilized to change the kinetic preference for the transformations of the sulfur ylides to synthesize 2,3-disubstituted dihydrobenzofuran derivatives. 239 Analogous to the sulfur ylides, the 2-halo-1,3-dicarbonyl compounds can also undergo a formal [4+1] annulation with salicylic aldehyde derivatives, such as the 2-hydroxyaryl-α,βunsaturated ketones, 2-hydroxyarylnitroalkenes, and 2-hydroxyarylimines, with K 2 CO 3 as the base, to produce a range of highly functionalized 2,3-dihydrobenzofurans with moderate to excellent yields. 240 The phosphine ylide, which is generated by the reaction of the nucleophilic phosphine with the electron-deficient allene, can also serve as a versatile 1,1-dipolar C1 fragment in a formal [4+1] annulation.…”

One-pot cascade synthesis of 2,3-disubstituted 2,3-dihydrobenzofurans via ortho-quinone methide intermediates generated in situ

“…4 The best developments in the past 10 years towards the synthesis of 2,3-disubstituted 2,3-dihydrobenzofurans were by cyclodehydration of 2-(2-hydroxyethyl)phenols, 5 asymmetric formal [4 + 1] cycloaddition of camphor-derived sulfonium salts with aldimines, 6 tandem Claisen rearrangement and intramolecular hydroaryloxylation of allyl aryl ethers, 7 intramolecular CH-insertion reactions, 8 palladium-catalyzed acyloxyarylation of benzofurans via dearomatization with arylboronic and carboxylic acids, 9 intramolecular aza-spiroannulation onto benzofurans using chiral rhodium catalysis, 10 intramolecular Michael addition-lactonization of [2-(a,b-unsaturated carbonyl)phenoxy]-acetic acids by organic and organometallic catalysts, 11 cerium ammonium nitrate-mediated oxidative dimerization of palkenylphenols 12 and through reactions of 2-hydroxyaryl-a,bunsaturated ketones with dimethylsulfonium carbonylmethylides. 13 The rst report of a 2,3-dihydrobenzofuran synthesis via an o-quinone methide (o-QM) intermediate was the C-H insertion reaction on the o-QM derived from (2-hydroxybenzyl)trimethylammonium iodide by dimethyl sulfoxonium methylide in base, followed by intramolecular substitution of trimethylamine, that gave the parent compound. 14 Aer fortyfour years, o-QM intermediates have been used again to synthesise 2,3-dihydrobenzofurans.…”