Mechanism of the keto-enol tautomerism in radical cations and gas-phase closed-shell systems

Abstract

The en:>l-keto tauta'cerism in radical cations has been ronsiderErl to involve a synmetry-forbidden l,3-hydrogen shift. An alternative process. involves t\\O ronsecuti ve 1,2-hydrogen shifts. The tili f ' s of the intennediate ions fomed by a l,2-hydrCX]en shift in the radical cations of phenol and the enol form of acetic acid have been calculatErl to be 220 and 191 kcal/nol, respectively., These tilii sindicate barriers to the keto-enol ~utanerj sm via t\\O Consecutive 1,2-hydrCX]en shifts of 50 and 47 kcal/nol, respectively, in go6d agreercent with previouslydetenninErl experimental values of 55 and 51 ,2:10 kcal/nol, respectively. Estimations of transition state energies for the tautanerism via tv.o ronsecuti ve 1,2-hydrCX]en shifts in the closErl shell systems , vinyl alrohol~acetaldehyde, H 2 c£H 3 ~ H3~2' and Cl1 3 Cl1==CcHfCl1 3 Cl1 2 0=cH 2 , indicate that the ass1..lITption of a synmetry-forbidden 1, 3-hydrCX]en shift is not requirErl.

Water‐Chain intervention in the ketonization of vinyl alcohol. An ab initio study

“…From the variation of the rate constant with temperature, the values of AH& = 11.23 kcal/mol and AS,:, = -13.26 cal/deg -mol have been obtained [ 5 ] . This small barrier for the enolketo tautomerism in aqueous solution contrasts with the high potential barrier of 74 kcal/mol, estimated for the same species in gas phase [6].…”

Palladium-Catalyzed Intermolecular Oxidative Cyclization of Allyltosylamides with AcOH: Assembly of 3-Pyrrolin-2-ones

“…First, intermediate A is formed by the reaction of Pd(OAc) 2 and N-tosylamide. 2c,4b,12 Then the N−Pd species A inserts to the alkene isomer of AcOH, 13 followed by the intermolecular Table 3. Pd-Catalyzed Intermolecular Oxidative Cyclization of (Homo)Allyltosylamides with AcOH a,b a Reaction conditions: 3 (0.10 mmol), Pd(OAc) 2 (10 mol%), AgOAc (0.20 mmol), AcOH (0.6 mL), Ac 2 O (0.6 mL) for 24 h. b Yields referred to isolated yield.…”

“…■ EXPERIMENTAL SECTION General Method. 1 H and 13 C NMR spectra were recorded on BRUKER DRX-400 spectrometer using CDCl 3 as solvent and TMS as an internal standard. The chemical shifts are referenced to signals at 7.26 and 77.0 ppm, respectively.…”

“…1 H NMR (400 MHz, CDCl 3 ) δ 7.79 (d, J = 8.3 Hz, 2H), 7.58 (d, J = 8.3 Hz, 2H), 7.33 (dd, J = 7.9, 6.9 Hz, 4H), 6.50 (d, J = 15.9 Hz, 1H), 6.19 (dt, J = 15.9, 6.0 Hz, 1H), 4.84 (s, 1H), 3.81 (t, J = 5.2 Hz, 2H), 2.44 (s, 3H). 13 ), 2.93 (q, J = 7.3 Hz, 2H), 2.41 (s, 3H), 1.31 (t, J = 7.3 Hz, 3H). 13 (E)-4-Methyl-N-(3-(m-tolyl)allyl)benzenesulfonamide (1j).…”

An efficient single-enzymatic cascade for asymmetric synthesis of chiral amines catalyzed by ω-transaminase

“…No additional enzymes, expensive cofactors or special measures are required for the purpose of pushing the equilibrium to the product side either by combining secondary irreversible reactions or removing volatile substances. In transamination, the generated ketone 3 (Scheme 1) is effectively removed by spontaneous tautomerization to 3-hydroxybenzoic acid 5, 28,29 thus allowing a theoretical yield of 100%.…”