Intramolecular Proton Research Articles

Electrophile-initiated selective ring transformations of cyclopropyl ketones

Electrophile-mediated cyclopropane cleavage in tricyclo[3.3.0.0 2,8]octan-3-one ( 1a) is increasingly directed towards the maximum bond overlap site in the following order of reagents: acetyl methanesulfonate, +Br - or I -; t-butyl-dimethylsilyl iodide; t-butyldimethylsilyl trifluoroacetate; trimethylsilyl trifluoroacetate. The latter reagent gives rise to one single regioisomer (→ 6a). Routine yields of isolated products lie between 78 and 87%. Increasing regioselectivity is governed by increasing electrophilic power and lowered nucleophilic strength of the reagents. Independent of these two factors, a C(4)- exo substituent in 1 directs the opening modes unidirectionally (→ 2b, 6b). Irrespective of the substitution pattern at C( 4) ( 1a- d), the cyclopropane moiety rearranges smoothly to olefinic ketones ( 8a- d) when the polymer-supported triflate analog Nafion-TMS is used in toluene at 80°. The reaction proceeds via intramolecular proton (deuterion) abstraction by the transient electron-rich enoxy double bond. This is the first fully proved case of such an intramolecular process. Aro-semibullvalenes ( 18, 22) similarly rearrange to aro-semibarrelenes (e.g. 21, 23) in the presence of Nafion-TMS. The latter rearrangement also takes place at room temperature when 18 or 22 are treated with commercial tetramethylsilane (TMS) and a catalytic amount of trifluoroacetic acid. An unknown impurity in the TMS reacts with the acid to form a powerful electrophilic composition. A cheap and convenient in situ preparation of TMS-triflate is described by mixing trifluoromethanesulfonic acid and TMS at room temperature.

Time-resolved fluorescence from biological systems: tryptophan and simple peptides

Four methods of applying mode-locked lasers to time-resolved fluorescence measurements in the subnanosecond region are compared. When time resolution below 100 ps is not required, the most precise and sensitive method is single-photon counting, and the application of this method to studies of time-resolved fluorescence of tryptophan in simple peptides is described. The dependence of lifetimes on pH and temperature are interpreted in terms of quenching by intramolecular proton and electron transfers.

Synthesis of βγ-unsaturated α-amino-acids

Saponification of methyl N-formylcycloalkylideneglycinates (3) gave N-formylcycloalk-1 -enylglycines (4) through migration of the double bond. The compounds (4) were converted into cycloalk-1-enylglycines (6) by acid hydrolysis. On the results of mechanistic studies it is supposed that the migration is initiated by intramolecular proton abstraction by the carboxylate ion at the γ-position. The method was extended to the synthesis of cycloalk-1-enylglycines containing heteroatoms in the ring [compounds (15)] and isodehydrovaline (17) in high yields.

Abbau von Palustrin zu (−)‐Dihydropalustraminsäure ((2R, 6S, 1′S)‐[6‐(1′‐Hydroxypropyl)‐2‐piperidyl]essigsäure) und Struktur von Palustrin und Palustridin. Mitteilung über Schachtelhalmalkaloide

Degradation of palustrin to (−)‐dihydropalustramic acid ((2R,6S,1′S)‐[6‐(1′‐hydroxypropyl)‐2‐piperidyl]acetic acid), and the structure of palustrin and palustridinThe structure of the macrocyclic alkaloid palustrin is shown to be 1a. Its piperidine unit can be obtained as (−)‐dihydropalustramic acid (6a) by the following sequence of degradation reactions (Scheme 1): catalytic hydrogenation of 1a followed by methylation and Hofmann degradation provides the allyl base 4. the regioselectivity of the Hofmann elimination is explained by intramolecular proton abstraction at C(3) by C(18)‐O−. Catalytic reduction of 4 and subsequent acidic hydrolysis yielded 6a and N, N‐dimethylputrescine (N,N‐dimethyl‐1,4‐butanediamine; 7). Loss of the N‐alkyl group in the formation of 6a occurs during the catalytic hydrogenation step. This interpretation is supported by the results of model experiments. The position of the double bond in 1a is deduced from the IR. spectrum of the bromo‐δ‐lactone 19 prepared by treatment of 1a with N‐bromosuccinimide at pH 4 (Scheme 3). Some of our previously published results on the degradation of dihydropalustrin (2a) are obviously at variance with the newly proposed structure for palustrin (1a). They can easily be explained by assuming a partial hydrogenolysis of the C(17)‐N(1) bond during the preparation of dihydropalustrin from palustrin. Periodate cleavage of dihydropalustramic acid methyl ester (6b) liberates propionaldehyde, which can be trapped by working at pH 7.5 (Scheme 2); at lower pH values it condenses rapidly with the simultaneously generated 3,4,5,6‐tetrahydropyridine derivative 15. The structure of the condensation product is proposed to be 16 on the basis of the isolation of its hydrogenation product, an isomeric dihydropalustramic acid (17).

The formation and photolysis of bis(fluorenyl)dimethylzirconium

Bis(fluorenyl)dimethylzirconium has been prepared from fluorene, methyllithium and zirconium tetrachloride by a new and convenient route. The compound was characterized by elemental analysis, proton NMR and mass spectrometry. Photolysis of bis(fluorenyl)dimethylzirconium in solution leads to cleavage of the methyl groups, with formation of methane and a bis(fluorenyl)zirconium-type compound of possible polynuclear nature. Infrared studies using specifically deuterated analogs have shown that this process occurs, at least in part, by intramolecular proton abstraction from theπ-coordinated fluorenyl rings.

ChemInform Abstract: THE RATES OF IONIZATION OF ARYLAMINO KETONES POSSESSING THE POTENTIALLY FOR INTRAMOLECULAR IMINE FORMATION AND INTRAMOLECULAR PROTON ABSTRACTION

Chemischer InformationsdienstVolume 6, Issue 39 Preparative Organic Chemistry ChemInform Abstract: THE RATES OF IONIZATION OF ARYLAMINO KETONES POSSESSING THE POTENTIALLY FOR INTRAMOLECULAR IMINE FORMATION AND INTRAMOLECULAR PROTON ABSTRACTION SANFORD N. GITEL, SANFORD N. GITELSearch for more papers by this authorC. DAVID GUTSCHE, C. DAVID GUTSCHESearch for more papers by this author SANFORD N. GITEL, SANFORD N. GITELSearch for more papers by this authorC. DAVID GUTSCHE, C. DAVID GUTSCHESearch for more papers by this author First published: September 30, 1975 https://doi.org/10.1002/chin.197539140AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue39September 30, 1975 RelatedInformation

Analysis of the temperature dependence of the NMR spectra in intra- and intermolecular exchanges in 1,4-dimethylhexahydro-l,2,4, 5-tetrazine with an electronic computer

1. A general program was compiled for the calculation of the NMR spectra in systems with intermolecular exchange. 2. The rates and parameters of the activation of intramolecular topomerization and intermolecular proton exchange in l,4-dimethylhexahydro-l,2,4,5-tetrazine (HHT) were determined by an analysis of the exchange broadenings in the PMR spectra on an electronic computer. 3. The limiting step of the indicated processes is inversion of nitrogen atoms. The peculiarities of the conformational structure of HHT are discussed.

Self-Diffusion Coefficients and Rotational Correlation Times in Polar Liquids. IV. Dichloromethane and Pyridine

Self-diffusion coefficients (D) have been measured in dichloromethane and pyridine from the freezing points to the normal boiling points. The data for CH2Cl2 are represented by D=(2.3± 0.6)10−3exp[−(2.40± 0.15)/RT] cm2sec−1, and the data for C5H5N are given by D=(5.9± 1.5) × 10−3exp[−(3.45± 0.15)/RT] cm2sec−1. Intramolecular proton, deuterium, and chlorine-35 relaxation rates were measured in dichloromethane from 178 to 310°K. The results demonstrate that the rotational correlation time is anisotropic; the proton and chlorine values differ by a factor of 2. The activation energy for relaxation is essentially the same for H, D, and Cl and equal to 1.81± 0.08 kcal mole−1. The present relaxation results and the relaxation data of Kintzinger and Lehn on pyridine are interpreted by means of the quasilattice random flight model generalized to the case of anisotropic rotators. The agreement between the calculated and observed relaxation rates is good for pyridine and fair for CH2Cl2. Calculated pre-exponential factors D0 are 1.8× 10−3 cm2sec−1 for CH2Cl2 and 2.5× 10−3 for C5H5N.

Cationic polymerization of cyclic dienes. X. Cationic polymerization of 1‐vinylcyclohexene and 3‐methyl‐1,3‐pentadiene

Abstract1‐Vinylcyclohexene (VCH), which has one of the double bonds in the ring and the other outside the ring, was synthesized and polymerized by cationic catalysts. The reactivity of VCH was very large in the polymerizations catalyzed by boron trifluoride etherate (BF3OEt2) and stannic chloride–trichloroacetic acid complex. Similar to other cyclic dienes, the polymerization of VCH was a nonstationary reaction having a very fast initiation step. The polymerization proceeded by either a 1,2‐ or a 1,4‐propagation mode in which vinyl group was always involved. Particularly when BF3OEt2 was used as a catalyst, an intramolecular proton or an intramolecular hydride ion transfer reaction took place, resulting in the formation of methyl groups in the polymer. The degree of polymerization of polymer formed was about 10. This indicates the preponderance of monomer transfer reaction. To investigate the reason for the high reactivity of cyclic dienes, cationic copolymerizations of VCH and 3‐methyl‐cis/trans‐1,3‐pentadiene (cis/trans‐MPD) was carried out. The relative reactivity of monomers decreased in the order VCH > trans‐MPD > cis‐MPD. On the other hand, the resonance stabilization of monomers decreased in the order VCH > trans‐MPD > cis‐MPD. Therefore, it could be considered that the monomer reactivity is mainly determined by the stability of carbonium ion intermediate. The relative stability of carbonium ion must be VCH > trans‐MPD > cis‐MPD. Thus the influence of the conformation of ion on its stability was clearly demonstrated.

Die reaktion von azoestern mit tetraalkyl-tetrazenen-(2)

Tetraalkyl-(2)-tetrazenes are attacked by azodicarboxylates at the dialkylamino nitrogen. By intramolecular proton abstraction, the betain 3 first formed is converted into the ylide 4 which then rearranges into 5. Kinetics of the reaction are investigated by UV spectroscopy; a mechanism is proposed.