Kinetic Resolution in the [2+2] Cycloaddition of Ketenes: An Experimental and Theoretical Study

Abstract

The kinetic resolution of Z and E olefins by [2+2] cycloaddition with ketenes allows the isolation of pure E olefin, as well as the synthesis of pure cis-cyclobutanones, starting from Z/E mixtures. A computational rationale for this kinetic difference is reported. The obtained difference of energy of activation matches with the experimental results.

Selecting Double Bond Positions with a Single Cation-Responsive Iridium Olefin Isomerization Catalyst

“…Transition metal catalysts with custom-tailored supporting ligands can facilitate selective isomerization, exemplified by systems capable of a single stereoselective double bond transposition. [11][12][13][14][15][16][17][18][19][20] The current paradigm for controlling selectivity is that for each different product, a new metal/ligand combination is needed ( Figure 1A). An alternative approach uses a single metal/ligand combination in conjunction with external additives to control the selectivity ( Figure 1B).…”

“…Switchable substrates were run in triplicate; substrates that did not show switchable behavior were run in duplicate.Volatile substrates 4-methyl-1-butene and 4-methoxy-1-butene were run in J-Young Teflon sealed NMR tubes and heated at 50 o C in order to prevent decrease in mass balance by evaporation of substrate. Isomers of 4-phenyl-1-butene (4a), 7,8 4-(4-methoxyphenyl)-1-butene (5a), 7,8 4-(2methoxyphenyl)-1-butene (6a), 8,9 4-(4-fluorophenyl)-1-butene (7a), 7,8 4-(4-bromophenyl)-1-butene (8a), 7,10 4-(4-chlorophenyl)-1-butene (9a),7 4-(2-chlorophenyl)-1-butene (10a),11 4-(4trifluoromethylphenyl)-1-butene (11a),7,8,12 ethyl 4-(4-carboxyphenyl)-1-butene (12a),13 4methyl-1-butene (13a),14 1-triisopropylsiloxy-3-butene (14a),15,16 2-(but-3-en-1-yl)-4,4,5,5tetramethyl-1,3,2-dioxaborolane (15a),[17][18][19] 5-hexen-2-one (16a),14 methyl pentanoate (17a),20 4-methoxy-1-butene (18a), 2-(but-3-en-1-yl)-2-methyl-1,3-dioxolane (19a),19 but-3en-1-yltrimethylsilane (20a),21 and but-3-en-1-yl acetate (21a),22 were assigned on the basis of olefinic H-H coupling constants and diagnostic chemical shifts in accord with literature reports.…”

Transition‐Metal‐Free Ring‐Opening Reaction of 2‐Halocyclobutanols through Ring Contraction

“…[25] Similar trend in reactivity was also observed in the addition of organocerium reagents to dichloro ketones. [26] Other approaches for the preparation of halocyclobutanols cover carbonyl group reduction, [27] double-bond hydroxylation, [28] epoxide opening, [29] and other means. [30] It is worth noting that the relative configuration of substituents for 2-bromocyclobutanols 3 has not been determined.…”

Substituted ketenes offer exceptional carbon bases in gas phase: Computational study by density functional theory method

“…[ 19 ] The most well‐known type of their reactions is the cycloaddition reaction. [ 20–24 ] The molecular orbitals (highest occupied molecular orbital [HOMO] and lowest unoccupied molecular orbital [LUMO]) are placed in the simple ketene in such a way that this molecule can participate in both nucleophilic and electrophilic addition reactions. [ 25 ] The experimental and theoretical investigations of ketene protonation in gas phase have been the research topic of a few scientific groups.…”