STEREOCHEMICAL PROPERTIES OF THE 1-CHLORO-1- PHENYL-2,5-DIMETHYL-2-PHOSPHOLENIUM ION AND DERIVED OXIDE AND PHOSPHINE

Abstract

The cycloaddition of phenylphosphonous dichloride and trans, trans-2,4-hexadiene, or the addition of chlorine to trans-1-phenyl-cis-2,5-dimethyl-3-phospholene, gave 1-chloro-1-phenyl-2,5-dimethyl-2-phospholenium chloride. This compound shows no evidence in its ³¹P and ¹H nmr spectra for the existence of cis, trans isomers, yet on hydrolysis or dehalogenation with magnesium the resulting oxide and phosphine, respectively, are seen to be isomer mixtures. This phenomenon is explained by a rapid equilibration of the cis, trans form of the I-chloro ion through a pentacovalent species. Structures of the oxides and phosphines were assigned by ¹H and ¹³C nmr relations. The 1-phenyl-cis-2,5-dimethyl-3-phospholenium ion and related compounds were also characterized.     

The effect of HMPA on the reactivity of epoxides,aziridines, and alkyl halides with organolithium reagents

A kinetic study of the effect of added HMPA cosolvent on the reaction of 2-lithio-1,3-dithiane (1), bis(phenylthio)methyllithium (2), and bis(3,5-bistrifluoromethylphenylthio)methyllithium (3) with methyloxirane (propylene oxide), N-tosyl-2-methylaziridine, and the several alkyl halides (BuCl, BuBr, BuI, allyl chloride) was carried out. Widely varied rate effects of HMPA on these SN2 substitutions were observed, ranging from >108 rate increases for 1 and butyl chloride to >103 rate decreases for 3 and methyloxirane. These reactions appear to go through separated ion pair intermediates, so a key effect is the ease of ion pair separation of the lithium reagent (3 > 2 > 1). Because 3 is already almost fully separated in THF, HMPA has no effect on the rate of halide substitution, but a large reduction is observed with the epoxide as substrate, a consequence of strong lithium assistance to the ring opening which is suppressed when excess HMPA is present. When ion pair separation is difficult (1), modest rate increases (104) are seen for epoxide opening, but very large increases are seen for aziridine (106) and alkyl halide reactions (108), for which lithium assistance is much less important. Reagent 2 shows more complicated behavior in reaction with the epoxide: 1-2 equiv of HMPA causes a small rate increase, while larger amounts cause a large rate decrease. Here the rate-accelerating effects of SIP formation are more nearly balanced with the rate-retarding effects of suppression of lithium catalysis.     

Reactivite des carbanions benzyliques : VIII. Etude de la structure d'alkyl-9 lithio-10 dihydro-9,10 anthracenes par rmn du proton et spectrometrie d'absorption electronique; influence du substituant,du solvant et de la temperature

The structure of the 9,10-dihydroanthracenyl anion and of a series of 9-alkyl-10-lithio-9-10-dihydroanthracenes (9-R-10-LiDHA, I–V where R = H, Me, Et, i-Pr, t-Bu) was studied in solution by electronic absortion spectrometry and proton magnetic resonance. Our electronic absorption results, in addition to those of other authors, show that the contact ion pairs (c.i.p.) have an absorption at λ_max}- 400 nm (I–III) and 415 nm (V) whereas the loose ion pairs (l.i.p.) absorb at λmax}- 450 nm (I–V). In the NMR the chemical shift of the proton para with respect to the carbanionic center was examined as a function of solvent (THF, THF/HMPA, and in some cases ether or pure HMPA) and temperature (+20 to ?40°C). The para proton is shielded significantly with regard to the aromatic protons of the hydrocarbon (Δδ(H_para) ca. 1–1.7 ppm). The weakest shielding was observed in ether, in agreement with the existence of c.i.p. The largest shielding (THF/HMPA or pure HMPA) is in connection with the presence of l.i.p. where the negative charge is less localised at position 10. Moreover, in the same solvent, and at the same temperature, Δδ(H_para) was observed to increase with the substituent bulk, up to the point that there are only l.i.p. present. As found previously (namely for the fluorenyl anion) the l.i.p./c.i.p. ratio increases when temperature decreases. The results of this structural study allow to rationalize the protonation stereochemistry of 9-alkyl-10-lithio-9,10-dihydroanthracenes in the above-mentioned solvents.     

Structural and vibrational characterization of the mono and dilithiated species derived from phenylacetonitrile in THF by infrared and Raman spectroscopy and density functional theory calculations

The structures and spectra of mono and dianionic species derived from PhCH2CN under the action of an organic base LHMDS or n-BuLi in THF solution have been investigated by vibrational spectroscopy and DFT calculations. The assignments previously proposed for the monoanion, the bridged, linear and dimeric monoanionic ion pairs compare well with the calculated ones. The addition of HMPA to a THF solution of PhCHCNLi leads to the formation of an HMPA solvated linear ion pair, distinguishable from the bridged ion pair by the wave number of the 8a v(CC) phenyl ring mode. The calculated structure of the phenylacetonitrile anion in the (PhCHCNLi, CH3Li) mixed dimer or 'Quadac' is very similar to that in the linear ion pair or in the dimer and to that observed by X-ray in (PhCHCNLi, [CH(CH9)2]2NLi) 'Quadac'. The structure of the anion is planar, indicating a charge delocalization from the benzene ring to the -CHCN group. The calculated spectra of the free, mono and dilithiated dianionic species compare well with the experimental ones of the species formed under addition of more than one equivalent of n-BuLi. The structure of the >C-C-CN2- group is very close to that of an imine. The v(CN) bands of the free, mono and dilithiated dianionic species are located at 1912, 1930 and 1890 cm(-1), respectively. The large wave number shift observed between the free monoanion and dianion (approximately 176 cm(-1)), in good accordance with the calculated one (170 cm(-1)) allows differentiating mono and dianionic species. The shifts observed for the 8a and 19a v(CC) phenyl ring modes, although much smaller, also allows discriminating the different species. These small shifts indicate a small variation of the electronic delocalization in the benzene ring in agreement with the calculations.     

Generation and stereoselective transformations of 3-phenylcyclopropene

A convenient and inexpensive approach to the generation of 3-phenylcyclopropenes is described. Reaction of these compounds with a range of dienophiles and dipolarophiles led to the stereoselective formation of [4+2]- and [3+2]-cycloadducts, which were exclusively exo-3-phenyl-cis-1,2-disubstituted cyclopropanes. Efficient trapping of 1-lithio-3-phenylcyclopropene with different electrophiles is also discussed. Ab initio calculations suggest that the lowest energy conformation of 3-phenylcyclopropene has the plane of the benzene ring perpendicular to the cyclopropene π-bond but with a low rotation barrier.     

Three-component condensation of Meldrum’s acid with 2-naphthylamine and esters derived from vanillin

Three-component condensation of Meldrum’s acid (2,2-dimethyl-1,3-dioxane-4,6-dione) with 2-naphthylamine and esters derived from vanillin involves intermediate formation of N-arylmethylidene-2-naphthylamines which are cleaved with Meldrum’s acid to give 5-arylmethylidene-2,2-dimethyl-1,3-dioxane-4,6-diones and arylmethylideneketenes. Reaction of the latter with 2-naphthylamine leads to formation of 2-methoxy-4-(3-oxo-1,2,3,4-tetrahydrobenzo[f]quinolin-1-yl)phenyl carboxylates.     

Probing Relaxation Dynamics in Five-Coordinate Dysprosium Single-Molecule Magnets

A new family of five-coordinate lanthanide single-molecule magnets (Ln SMMs) [Dy(Mes*O)₂(THF)₂X] (Mes*=2,4,6-tri-tert-butylphenyl; X=Cl, 1 ; Br, 2 ; I, 3 ) is reported with energy barriers to magnetic reversal >1200 K. The five-coordinate Dy^III ions have distorted square pyramidal geometries, with halide anions on the apex, and two Mes*O ligands mutually trans- to each other, and the two THF molecules forming the second trans- pair. These geometrical features lead to a large magnetic anisotropy in these complexes along the trans-Mes*O direction. QTM and Raman relaxation times are enhanced by varying the apex halide from Cl to Br to I, or by dilution in a diamagnetic yttrium analogue.     

Synthesis of 4,6-diaryl-1-benzyl-6-hydroxy-5,5-dimethyl-2-oxopiperidine-3-carbonitriles and their analogs via a modified Reformatsky reaction

Organozinc compounds obtained from 1-aryl-2-bromo-2-methylpropanone and zinc react with N-benzyl-3-aryl-2-cyanoacrylamides or N-[6-(2-cyano-1-oxo-3-phenylprop-2-enylamino)hexyl]-2-cyano-3-phenylacrylamide to give 4,6-diaryl-1-benzyl-6-hydroxy-5,5-dimethyl-2-oxopiperidine-3-carbonitriles or 1,6-bis(6-aryl-3-cyano-6-hydroxy-5,5-dimethyl-2-oxo-4-phenylpiperidyl)hexanes as a single isomer with trans-located piperidine hydrogen atoms.     

Resolution of 4-oxoazetidin-2-yl benzoate by inclusion crystallization with an optically active host compound

4-Oxoazetidin-2-yl benzoate was resolved efficiently by an inclusion complexation with a chiral host compound, (R,R)-(−)-trans-4,5-bis(hydroxydiphenylmethyl)-1,4-dioxaspiro[4.5]decane. The phenyl substituent on the β-lactam ring was found to play an important role in an efficient chiral recognition in the inclusion crystals.     

Amide rotamers of N-acetyl-1,3-dimethyltetrahydroisoquinolines: synthesis, variable temperature NMR spectroscopy and molecular modelling

Mercury(II)-mediated ring closure of N-[1-(2-allyl-3-benzyloxy-4,6-dimethoxyphenyl)ethyl]acetamide 9 afforded N-acetyl-5-benzyloxy-6,8-dimethoxy-1,3-trans-dimethyl-1,2,3,4-tetrahydroisoquinoline 8. The product was shown to exist as a mixture of amide rotamers by NMR spectroscopy, since signals coalesced at higher temperatures. Variable temperature NMR spectroscopy and molecular modelling were used to investigate these rotamers and gave average values for the barrier of rotation in the range of 15-16 kcal mol⁻¹. 2-[2-[1-(Acetylamino)ethyl]-6-(benzyloxy)-3,5-dimethoxyphenyl]-1-methylethyl methanesulfonate 17 was also cyclized with sodium hydride to afford the same rotameric products with the same tetrahydroisoquinoline skeleton, but as a mixture of 1,3-trans- and cis-dimethyl isomers.     

13C NMR coupling constants in delocalized organo-alkali metal compounds. Models of polymerization systems

2,5-Diphenyl-2,5-dipotassiohexane, 2-lithio-4,4-dimethyl-2-phenylpentane, and 1-lithio-2,5,5-trimethylhexene-2 have been prepared, all labelled with¹³C in the position adjacent to the alkali metal atom. The¹³C NMR spectra of these compounds have been measured and the¹³CC coupling constants found for the charged atom. The first two compounds have coupling constants consistent with an sp² hybridized C_α, with relatively little effect of the charge on the coupling constant. The third compound, when dissolved in either THF or benzene, gave much smaller coupling constants, which are more difficult to interpret.     

Regiointegrity of carbanions derived by selective metalations of dimethylpyridines and -quinolines

Metalation of 2,4-dimethylpyridine and -quinolines by strong basic reagents in ethyl ether in the absence of HMPA affords 2-lithiomethyl derivatives regardless of the reaction length. The use of THF in such metalations promotes the formation of the 2-lithiomethyl reagents which isomerize to the more thermodynamically stable 4-lithiomethyl derivatives after relatively long reaction periods or in the presence of amines or an excess of the parent heterocycle. The latter derivatives appear to be formed directly from the heterocycles in ammonia or in the presence of HMPA. The results are discussed in terms of “coordination-only” versus “acid-base” limiting mechanisms for metalations as a function of ion pairing. NMR spectra for certain of the carbanions in ethyl ether and THF are described which support the above concepts. Related metalations of 2,4-dimethylquinoline-N-oxide give only the 2-lithiomethyl derivative. Similar reactions of 7-hydroxy-2,4-dimethyl-1,8-naphthyridine lead in synthetically useful yields to derivatization of the 2- and 4-methyl groups via dianions by using n-butyllithium in ethyl ether and sodium amide in liquid ammonia, respectively, followed by the addition of appropriate electrophiles.     

Stereoselective functionalization of 1-alkoxy-2-(phenylethynyl)cyclopropanes <Emphasis Type="Italic">via</Emphasis> lithiation and subsequent reactions with electrophilic reagents

trans-1-Alkoxy-2-(phenylethynyl)cyclopropanes undergo lithiation at the hydrogen atom in the α-position to the triple bond on treatment with BuLi in THF at–(65—70) °C. The resulting organolithium derivatives react with acetaldehyde, acetone, dimethyl disulfide, and methyl chloroformate giving the corresponding alcohols, sulfides, and esters with the yields up to 69% with complete retention of cyclopropane ring stereoconfiguration. The obtained methyl 3-alkoxy-2,2-dimethyl-1-(phenylethynyl)cyclopropanecarboxylates and the corre-sponding acid readily undergo ring opening with addition of water molecule or HCl.     

Polylithiumorganic compounds. Part 29: C,C Bond cleavage of phenyl substituted and strained carbocycles using lithium metal

The reaction of phenyl substituted cyclopropanes phenylcyclopropane and 1,1-diphenylcyclopropane, phenyl substituted bicyclobutanes 1-phenylbicyclobutane, 1-methyl-3-phenylbicyclobutane, 1-methyl-2,2-diphenylbicyclobutane, as well as phenyl substituted spiropentanes phenylspiropentane and 1,1-diphenylspiropentane with lithium metal or lithium di-t-butylbiphenyl (LiDBB) was investigated. Under suitable reaction conditions and choice of solvent in all cases cleavage of the single bond next to the activating phenyl group was observed. The dilithiumorganic compounds thus obtained are sufficiently stable and can be trapped with electrophiles. Lithium hydride elimination is observed as follow-up reaction only in a few cases. The corresponding anions of the strained ring systems 1-lithio-2,2-diphenylcyclopropane, 1-lithio-3-phenylbicyclobutane, 1-lithio-3-methyl-2,2-diphenylbicyclobutane, and 1-lithio-4-phenylspiropentane, which can be obtained by lithium bromine exchange or by metalation of the unsubstituted carbocycle, do not show any cleavage upon reaction with lithium metal.     

Investigation of reactions of the organozinc reagents prepared from zinc and dialkyl dibromomalonates with the derivatives of 2-arylmethyleneindan-1,3-dione and 5-arylmethylene-2,2-dimethyl-1,3-dioxane-4,6-dione

Organozinc compounds prepared from dialkyl dibromomalonates and zinc react with 2-arylmethyl-eneindan-4,6-diones, 5-arylmethylene-2,2-dimethyl-1,3-dioxane-4,6-diones, as well as with 2-[4-(1,3-dioxoindan-2-ylidenemethyl)phenyl]methyleneindan-1,3-dione and 5-[4-(2,2-dimethyl-4,6-dioxo-1,3-dioxane-2-ylidenemethyl)phenyl]methylene-2,2-dimethyl-1,3-dioxane-4,6-diones to form dialkyl 3-aryl-1′3′-dioxaspiro(cyclopropane-2,2′-indan)-1,1-dicarboxylates, dimethyl 3-aryl-6,6-dimethyl-5,7-dioxa-4,8-dioxaspiro[2,5]octan-2,2-dicarboxylates, dialkyl 2-{4-[3,3-bis (alkoxycarbonyl)-1′,3′-dioxaspiro(cyclopropane-2,2′-indan)-1-yl]phenyl}-1′,3′-dioxaspiro[cyclopropane-2,2′-indan]-1,1-dicarboxylates, and dialkyl 2-{4-[2,2-bis(alkoxycarbonyl)-6,6′-dimethyl-4,8-dioxo-5,7-dioxaspiro[2,5]oct-1-yl]phenyl}-6,6-dimethyl-4,8-dioxo-5,7-dioxaspiro[2,5]octan-1,1-dicarboxylate respectively.     

A novel redox reaction between 8-Aza-5,7-dimethyl-2-trifluoromethylchromone and alkyl mercaptoacetates. Facile synthesis of CF3-containing 2-pyridone derivatives

8-Aza-5,7-dimethyl-2-trifluoromethylchromone reacts with alkyl mercaptoacetates in the presence of triethylamine to give pyrido derivatives of 2-oxa-7-thiabicyclo[3.2.1]octane, which undergo the reductive ring opening to alkyl 2-[[3-(4,6-dimethyl-2-oxo-1,2-dihydropyridin-3-yl)-3-oxo-1-(trifluoromethyl)propyl]sulfanyl]acetates.The latter can be also obtained directly from 8-aza-5,7-dimethyl-2-trifluoromethylchromone and behave as the masked alpha,beta-unsaturated ketone, 4,6-dimethyl-3-(4,4,4-trifluorobut-2-enoyl)pyridin-2(1H)-one. This compound was independently synthesized from 3-acetyl-4,6-dimethyl-2-pyridone, and its synthetic potential was studied. A wide variety of 2-pyridone derivatives containing the CF(3) group have been prepared in good to moderate yields.     

Mass spectrometry in structural and stereochemical problems—CLXXXV Effect of phenyl group in the mass spectra of trans-10-phenyl-2-decalone and trans-10-phenyldecalin

With the use of deuterium labeling and metastable ion measurements, the major fragmentation pathways of trans-10-phenyl-2-decalone (II) have been deduced. A comparison with trans-10-phenyldecalin (IV) demonstrated the almost complete domination of the phenyl group in directing the electron-impact promoted decomposition of II. In fact, in contrast to the spectra of the methylated analogs, only one fragmentation pathway is uniquely associated with the carbonyl function. The substitution of a phenyl group at the ring junction in IV has permitted the recognition of definitive fragmentation pathways for this compound also. Such definition has not previously been possible for unsubstituted alicyclic hydrocarbons. The formation of an abundant tropylium ion from both II and IV has been examined, but its genesis is too complicated to be accurately defined from the labeling data at hand.     

Neopentylallylsodium

Neopentylallylsodium (NpANa) has been prepared by the reaction of neopentylallyllithium with an equivalent amount of sodium 2,2-dimethyl-1-butoxide in hydrocarbon solvent. NpANa is stable in diethyl ether and THF solvents for extended periods of time, and proton NMR and UV data are reported for NpANa in THF at various temperatures. A more substantial degree of ionic delocalization is indicated for NpANa as compared to NpALi and apparently is greater for the trans isomer of NpANa. UV absorption maxima for NpANa and NpALi are explained in terms of cis/trans ratios rather than in terms of ion pairing.     

(Z)-1-alkylidene- and 1-arylmethylidene-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ides and their cycloaddition to N-arylmaleimides

The reaction of (Z)-1-arylmethylidene-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ides with para-substituted N-arylmaleimides at 110°C is cis-stereoselective [cis/trans-adduct ratio ??(9?C10): 1]. Under analogous conditions, the conversion of (Z)-1-(2,6-dichlorophenylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide in the reaction with N-(4-methoxyphenyl)maleimide in 6-7 h did not exceed 1?C2%. The cycloaddition of (Z)-1-ethylidene- and (Z)-1-(2-methylpropylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ides to N-arylmaleimides, regardless of the substituent in the phenyl group of the latter, gave preferentially the corresponding trans-adducts, which cannot be rationalized only by steric effect of substituents in terms of the concerted mechanism.     

Effect of allylic strain on the conformations of diphenyl-substituted tetrahydro-1,3-oxazin-2-ones and hexahydropyrimidin-2-ones

The conformations of the cis and trans isomers of 4,6-diphenyl-, 4,5-diphenyl- and 5,6-diphenyltetrahydro-1,3-oxazin-2-one and 4,5-diphenylhexahydropyrimidin-2-one, and of some of their N-substituted derivatives, have been studied by ¹H NMR. Conformers with 4a, 6e-, 4a, 5e- and 5a, 6e-phenyl groups are preferred in the respective isomers of the N-H oxazinones, confirming a half-chair conformation of the ring. Allylic strain caused by N-substituents shifts strongly the a,e?e, a equilibria in trans-4,6-diphenyl- and cis-4,5-diphenyl-oxazinones, but only moderately the e,e?a,a equilibria in the compounds with trans-vicinal phenyl groups. In the latter, the diaxial conformation is preferred only in the case of bulky N-substituents. The diaxial conformation is more favoured in the trans-4,5-diphenylpyrimidones.