Electrophilic substitution at saturated carbon. XLIII. Alkylammonium carbanide ion-pair reorganization reactions in base-catalyzed 1,3-proton transfer in an indene system

Abstract

For study of base-catalyzed proton transfer, (-)-3-/-butyl-l-methylindene-l-/z ((-)-I-h), (-)-3-?-butyl-1 -methylindene-1 -d ((-and (+)-l-f-butyl-3-methylindene-1 -h ((-f-)-II-A) of maximum rotations were prepared. Comparisons of their optical rotatory dispersion curves and those of their ketonic precursors, (-)-(Z?)-3methyl-1-indanone ((-)-(/?)-IV) and (-)-3-/-butyI-l-indanone ((-)-(S)-VI), established that (-)-l-h and (+)-ll-h possess opposite configurations. Optically pure ketones (-)-VI undeuterated at the chiral center, deuterated at the chiral center, and dideuterated at the position a to the ketonic group differ in rotations by unusually large amounts up to 300% at 390 µ. This effect is attributed mainly to the difference in steric requirements of H and D, and the consequent change in dihedral angle about the C2-C3 bond of the deuterated and nondeuterated indanones. Equilibrium constants for I <=± II were found to be 5.99-6.04 at 102°( r-butyl alcohol-triethylenediamine), 6.64-6.69 at 48°( 10 mol % methanol-90 mol % dimethyl sulfoxide-triethylenediamine), and 7.50-7.60 at 25 °(tetrahydrofuran, 2.0 M in «-propylamine). Under conditions that II was stable to exchange, racemization, or isomerization, I was isomerized to II; the two isomers were separated and analyzed for isotopic exchange and racemization. In all runs with amine catalysts and with transfer of either hydrogen or deuterium with solvents ranging from dimethyl sulfoxide-r-butyl alcohol to benzene (-)-I gave (+)-II of 97-100% optical purity, and recovered (-)-I was 98-100% optically pure. Proton transfer involved almost exclusively only one face of the allylic anion. With I-h in r-butyl alcohol-O-rf with triethylenediamine as base and in the presence of deuterated amine salt as a primary isotope pool, the (-f-)-II produced had undergone only 0.35% isotopic exchange. In dimethyl sulfoxide, 1.0 M in tbutyl aicohol-O-d with the same base and salt, the (+)-II had undergone 1.2% isotopic exchange. In tetrahydrofuran, 0.61 M in «-propylamine, l-d gave II that was 95% exchanged, whereas with I-H and deuterated amine in the same solvent the II produced was 36% exchanged. Recovered I from these experiments gave ke!ka (rate constant for isotopic exchange over that for racemization) values >7.5. These experiments demonstrate that in the alkylammonium carbanide ion pair, alkylammonium ions reorganize enough to provide for extensive isotopic exchange, and that protium is captured by the anion more efficiently than deuterium. In benzene, 0.10 M in piperidine, l-d gave II with 27% isotopic exchange, whereas in benzene, 0.10 M in deuterated piperidine, l-h gave II with only 13% isotopic exchange. In this ion-pair intermediate, the dialkylammonium ion moved across the t cloud of the allylic anion and donated a proton or deuteron to the new site faster than the ammonium ion rotated. The anion of these contact ion-pair intermediates appears mainly to hydrogen bond no more than one hydrogen at a time.the first elegant kinetic results of Bergson, et al.f ap-(1) This r...

Synthetic Route to 4,4a‐ and 3,4‐Dihydroxanthones through [4+2] Cycloaddition and Base‐Assisted Sigmatropic Rearrangement

“…From the classical work of Almy and Cram we know about the [1,3]‐H shift in a number of indenes under the action of base . On the basis of their process kinetics studies, the authors established an ion‐pair proton transfer without its full transition into an amine.…”

“…From the classical work of Almy and Cram we know about the [1,3]-H shift in a number of indenes under the action of base. [10] On the basis of their process kinetics studies, the authors established an ion-pair proton transfer without its full transition into an amine. Summarizing our experimental data we can assume a similar amine-assisted isomerization of the 4,4a-dihydroxanthones, in which the amine coordinates to the proton and thereby reduces the energy barrier of the reaction.…”

vic-Iodothiocyanates and iodoisothiocyanates. Part 4. The synthesis of 2-substituted-2-thiazolines

“…The infrequency of metal-halogen exchange reactions between organo-lithium reagents and alkyl chlorides was illustrated by the reaction of 1-chloro-3-isothiocyanatopropane with butyl-lithium. In this case the butyl ca rbanion attacked the isot hiocyanato-carbon atom to give N-(3-chloropropyl) thiopentanamide (33) (93 yo) which on heating gave 2-butyl-5,6-dihydro-4H-1,3-thiaziniuni chloride (34) as a dark red water-soluble solid. Treatment of the salt with sodium hydrogencarbonate gave 2-butyl-5,6-dihydro-4H-l,3-thiazine (35) in 71% overall yield.…”

“…Workup gave N-(3-chloropropyl)tliiopentanamide (33) (0.40 g, 93@/,) as an oil; 6 0.93 (t, Me), 1.50 (m, CH,), 2.22 (m, 2'-H2), 2.90 ipoorly resolved t , W , 10.5 Hz, C(:S)CH,], 3.39 (poorly resolved t , T V J 14 Hz, CH,Cl), 3.80 (poorly resolved t , W t 13.5 H z , CH,N), ancl 10.42 (br s, NH). Attempted distillation (Kugelrolir) (105 "C a t 1 mmHg) of the uncyclized product (33) gavc 2-butyl-5;6-dihydro-4H-1,3thiaziniuni chloride (34) as a dark-red water-soluble solid. Treatment of the salt with saturated sodium hydrogencarbonate followed by partition with ether gave 2-butyl-afforded: (i) starting material (24 iiig, 12%) : (ii) the cisiodoisothiocyanate (37) (18 mg, 9%) : and (iii) the butyl-2thiazoline (12) (60 mg, 41%).…”

Isoracemization of N-carbobenzoxyamino acid ester derivatives

“…The elemental compositions of m/e 328.0983 and 256.1173 ion were determined by Dr. Foltz and found to be CisHisNOaS and CisHisNS, respectively. "The triethylamine concentration was 0.31 M. 6The active ester concentration was 0.0435 M. c The concentration of methanol-O-d was 2.3 M. 4 The reaction was carried out at a constant temperature of 32°. ec 2, dimethylformamide.…”