Regioselective Reactions of 1-Alkylidene-2-oxyallyl Cations with Furan:  Control of [4 + 3] Cycloaddition, [3 + 2] Cycloaddition, and Electrophilic Substitution

Abstract

The ring opening of alkylidenecyclopropanone acetal under acidic conditions produces the 1-alkylidene-2-oxyallyl cation as an intermediate, which reacts with furan to give the [3 + 2] and [4 + 3] cycloadducts as well as an electrophilic substitution product. The product distribution is controlled by the oxy substituents of the cation and by the solvent employed.

(3+2)-Cycloaddition Reactions of Oxyallyl Cations

“…36 While the reaction of 131 with excess furan delivered a mixture of (4+3) cycloadducts and rearranged products from the (3+2) cycloadducts, the reaction with 2,3-benzofuran 132 furnished (3+2) cycloadduct 133 as a single regioisomer in 76% yield.…”

Recent developments in the reactivity of methylene- and alkylidenecyclopropane derivatives

“…48 In contrast, when furan was employed as the nucleophilic partner, the reaction with an alkylidenecyclopropanone acetal under acidic conditions led to the formation of the corresponding formal [3þ2] and [4þ3] cycloadducts, as well as electrophilic substitution products. 49 In 2007, Huang et al reported the acylation of alkylidenecyclopropanes mediated by a stoichiometric amount of AlCl 3 , allowing the synthesis of a variety of a,b-unsaturated ketone derivatives with high stereoselectivity to be achieved. 50 This process could be applied to a number of acyl chlorides and alkylidenecyclopropanes, and the best results are collected in Scheme 32.…”

Addition Reactions: Cycloaddition

“…57 3-Substituted 1,2-diphenylcyclopropenes and 3,3-disubstituted cyclopropenes reacted with carbonyl ylides, derived by dirhodium tetraacetate-catalysed decomposition of diazocarbonyl precursors, to produce 8-azatricyclo[3.2.1.0 2,4 ]octanes and 9-oxatricyclo[3.3.1.0 2,4 ]nonanes. 58 Chiral 5-ethoxy-3-p-tolylsulfinylfuran-2(5H )-ones (55) reacted with 2-benzopyrylium-4-olate (56) to give 4,10-epoxybenzo [4,5]cyclohepta[1,2-c]furan-3,9-diones (57,58) in good to moderate yields with high regioselectivity (Scheme 15). 59 2,6-Bis(oxazolinyl)pyridine-lanthanoid complexes catalysed the asymmetric 3 + 2-cycloaddition reactions of 2-benzopyrilium-4-olates with 3-(alk-2enoyl)-2-oxazolidinones to yield cycloadducts, substituted (2-oxazolidinoyl)carbonyl-8-oxabenzo[c]bicyclo[3.2.1]octan-2-ones with high enantioselectivity (96% ee) and ee endo selectivity (>99:1).…”

“…150 The CANinitiated aza-Diels-Alder reaction of N -arylimines with N -vinylpyrrolid-2-one or N -methyl-N -vinylacetamide formed the corresponding 2,4-cis-4-amido-N -yl tetrahydroquinoline derivatives in good yields. 151 A DFT investigation of the Diels-Alder reactions of substituted triazolo [3,2-d] [1,4,2]diazaphospholes with buta-1,3-diene and isoprene revealed concerted mechanisms via asynchronous transition states. 152 The inverse-electron-demand Diels-Alder reactions of 3-methylsulfinyl-6-methylthio-1, 2,4,5-tetrazine and 3-(benzyloxycarbonyl)amino-6-methylsulfinyl-1,2,4,5-tetrazine are regioselective, producing a single cycloadduct in each case.…”

“…164,165 The enantioselective [Rh(cod){(S)-xylyl-binap}]BF 4catalysed 2 + 2 + 2-cycloaddition of 1,6-diynes with α-methylene lactones and cyclic ketones formed chiral spirocyclic compounds. 166 Mono-and di-nuclear titaee nium complexes of p-t-butylthiacalix [4]arene are efficient catalysts for the 2 + 2 + 2-cyclotrimerization of terminal alkynes to produce 1,3,5-trisubstituted benzenes regioselectively. 167 The diastereoselective cobalt(I)-mediated 2 + 2 + 2-cycloaddition of allenediynes (125) The nickel-catalysed 3 + 1 + 1-cycloaddition of alkenyl Fischer carbene complexes with methylenecyclopropanes produced the methylenecyclopentanone in high yields.…”