Allylic Carbanions Research Articles

Synthesis of triphenylsilyl‐ and triphenylmethyl‐telechelic polyisobutylene: An approach to the synthesis of multi‐ion telechelic ionomers

AbstractTriphenylsilyl‐ and triphenylmethyl‐telechelic polyisobutylene (PIB) were prepared by lithiation of three‐arm star PIBs carrying either olefinic or tert‐alkyl chloride end groups, followed by reaction with triphenylsilyl chloride or triphenylcarbenium ion, respectively. Since the lithiated intermediate is a substituted allylic carbanion, the chain end also possesses a double bond which is located β‐γ relative to the silyl or triphenylmethyl group. The phenyl groups were incorporated into the polymers to provide extra sites for sulfonation, in addition to the double bond, to enable the synthesis of multi‐ion telechelic ionomers. 1H‐ and 13C‐NMR spectroscopy showed that triphenylsilylation and triphenylmethylation were essentially quantitative when applied under the prescribed conditions to either the model compound, 2,4,4‐trimethyl‐1‐pentene, or to the telechelic PIBs. It was observed that exhaustive sulfonation of these materials using acetyl sulfate or chlorosulfonic acid yielded only about 50% sulfonation of the available sites. This suggests that sulfonation of closely adjacent, multiple sites within the same molecule fails due to deactivation of the remaining sites after one or perhaps two sulfonations. However, the triphenylsilyl‐ and triphenylmethyl‐telechelic PIBs represent novel prepolymers which can perhaps be derivatized by some method other than sulfonation, and the general concept for producing telechelic ionomer precursors with multiple sulfonation sites may prove successful with other moieties containing spacer groups between sites. © 1993 John Wiley & Sons, Inc.

Synthetic utilization of highly stereoselective conjugate addition reactions of phosphorus and sulfur stabilized allylic carbanions

Abstract

A facile synthesis of 1,5-dienes by a regioselective allylation of the allylic carbanions generated from allyl phenyl selenides.

Allyl-allyl or benzyl coupling reactions were effected by allyl carbanions, generated from allyl phenyl selenides and n-butyllithium and allylic or benzylic halides. The ambident selectivities of the allyl carbanions are depending in the solvent system.

π‐アリルパラジウム錯体の見かけ上の電荷反転 アリルアルコール類によるカルボニル‐アリル化反応への応用

Palladium-catalyzed carbonyl allylation by allylic alcohols with SnCl2 smoothly proceeds in aqueous medium under air. The actual allylating agent in the carbonyl allylation by allyl alcohol in dry medium is allyltrichlorotin, which is prepared via (1) oxidative addition of allyl alcohol to Pd (0) complex with SnCl2, (2) insertion of SnCl2 to π-allylpalladium complex, followed by (3) reductive elimination of π-allylpalladium trichlorostannate. Allylic alcohols, preparing π-allylpalladium complexes, function as synthons of allylic carbanions. In other words, this implies the apparent charge reversal of electrophilic π-allylpalladium complexes. The carbonyl allylation by allylic alcohols can achieve high chemo-, regio-, and diastereoselection by the choice of solvent, and can be applied to chelation-controlled diastereoselection in polar solvents.

STUDIES ON ORGANOPHOSPHORUS COMPOUNDS XLIV. STRUCTURAL EFFECT OF ELECTROPHILES ON THE REGIOSELECTIVITY OF CARBANION DERIVED FROM DIALKYL ALLYLPHOSPHONATES

Abstract For the evaluation of the structural effect of electrophiles on the regioselectivity of ambident anions, the reaction of phosphoryl allylic carbanion with p-substituted benzaldehydes was investigated.

ChemInform Abstract: Preparation of 3‐Methoxy‐1‐trimethylsilyl‐1,3‐dienes Using a One‐Pot Wittig‐Horner Reaction.

AbstractChlorodiphenylphosphine (I) reacts with the dimethyl acetals (II) to give the phosphine oxides (III) which are silylated via their allylic carbanions, forming the compounds (V).

ChemInform Abstract: Allylic Alcohols as Synthons of Allylic Carbanions. Palladium‐Catalyzed Carbonyl Allylation by Allylic Alcohols with SnCl2.

AbstractThe palladium‐catalyzed allylation of carbonyl compounds such as (II) by allylic alcohols such as (I) with SnCl2 proceeds at 25 °C in DMI to give the homoallylic alcohols (III).

Allylic alcohols as synthons of allylic carbanions. Palladium-catalyzed carbonyl allylation by allylic alcohols with tin dichloride

L'allylation des aldehydes est chimioselective et a ete effectuee en presence du groupement cetone

ChemInform Abstract: Regioselective Carboxylation of Silicon‐Stabilized Allylic Carbanions and the Synthetic Utility of 2‐Silyl‐3‐butenoates.

AbstractCarboxylation of the lithiated allyltriorganosilanes (I) gives isomeric mixtures of the acids (III) and (IV); in most cases a moderate γ‐regioselectivity is observed.

Preparation of bicyclic compounds from the products of conjugate addition of allylic sulphoxide and phosphine oxide carbanions to cyclopent-2-enones

The conversion of the compounds obtained from the conjugate addition of the carbanions of allylic sulphoxides and phosphine oxides into bicyclo[3.3.0]octanes, bicyclo[2.2.1]heptanes, and bicyclo[3.2.1]octanes whose configurations reflect those of the starting compounds is described.

Stereochemical and Mechanistic Aspects of the Aprotic Conjugate Addition Reactions of the Carbanions of Octenyl Sulfides and Octenyl Thiocarbamates With 4-Tert-Butoxycyclopent-2-Enone in the Presence of Hexamethylphosphoric Triamide

The carbanions of (E)- and (Z)-1-(pheny1thio)oct-2-ene, (E)-1-(methy1thio)- and 1-(t-butyl- thio )oct-2-ene, N,N-dimethyl S-[(E)-oct-2-enyllthiocarbamate and (E)-oct-2-enyl benzothiazole undergo conjugate addition to 4-t-butoxycyclopent-2-enone in the presence of hexamethyl - phosphoric triamide ( hmpa ) in tetrahydrofuran at -70� to give as predominant products diastereomeric mixtures of syn and anti allylic sulfides arising from reaction through C1 of the octenyl carbanions. Also formed in some cases are small amounts of diastereomeric mixtures of syn and anti vinylic sulfides arising from reaction through C3 of the octenyl carbanions. In the absence of the hmpa, carbonyl addition is the major reaction pathway of the carbanions of each of the (E)- and (Z)- octenyl thiocarbamates. The constitutions and stereostructures of all the products have been established through chemical shift and coupling constant correlations of their IH n.m.r. data obtained at 400 MHz. The relative proportions of the regioisomeric allylic and vinylic sulfides are dependent both upon the nature of the non-allylic substituent attached to the sulfur atom, and the geometry of the double bond in the starting octenyl sulfide. While there is no apparent connection between the electronic properties or sizes of the non-allylic substituent and the diastereomer ratios of the allylic and vinylic sulfides, it is noted that the (2)-(phenylthio) octene delivers an allylic sulfide mixture enriched in the syn isomer. It is concluded that the carbanions are configurationally stable at-70� and that the configurations of the vinylic sulfides reflect the configurations of the carbanions from which they are derived. It is also concluded that the reactions proceed under orbital control, as this best accounts for the formation of the vinylic sulfides and is in accord with the results of STO-3G calculations carried out on a series of sulfur-bearing allylic carbanions . The likely angle of attack of the carbanions on the enone system is briefly discussed in terms of a published model relating to the attack of a simple nucleophile on an electrophilic double bond.

The Aprotic Conjugate Addition-Reactions of the Carbanions of Octenyl Sulfides and Thiocarbamates With γ-Crotonolactone- Stereochemical and Mechanistic Aspects of Reactions Conducted in the Absence and Presence of Hexamethylphosphoric Triamide

The lithiated carbanions of (E)- and (Z)-1-(phenylthio)oct-2-ene, (E)-1-(methylthio)oct-2-ene, S-[(E)-oct-2-enyl] N,N-dimethyl( thiocarbamate ), S-[(a-oct-2-enyl] N,N-dimethyl- ( thiocarbamate ), and (E)- and (Z)-1-(phenylsulfony1)oct-2-ene undergo conjugate addition to γ-crotonolactone (but-2-en-4-olide) in tetrahydrofuran at -70� to give as predominant products, syn and anti allylic sulfides, thiocarbamates and sulfones arising from reaction through C1 of the octenyl carbanions . Also formed are smaller amounts of syn and anti vinylic sulfides, thiocarbamates and sulfones arising by reaction through C3 of the octenyl carbanions. The carbanions of the octenyl sulfones give smaller amounts of the vinylic products than do the other carbanions. In the presence of hexamethylphosphoric triamide (hmpa), the relative amounts of the latter compounds are depressed in favour of the former. The diastereoselection of these reactions is significantly smaller than the corresponding reactions involving 4-t-butoxycyclopent-2-enone. The constitutions and stereostructures of all the products was established by analysis of 1H n.m.r. data and n.O.e. difference experiments conducted at 400 MHz. The enhancement of the amounts of the allylic at the expense of the vinylic compounds induced by the hmpa is tentatively ascribed to frontier molecular orbital effects, and suggests that the operation of chelation and charge control in the reactions of related allylic carbanions with carbonyl compounds is less important than is generally considered to be the case. The various factors which cause carbanions to undergo conjugate addition to α β-unsaturated carbonyl compounds and the role played by the hmpa in these reactions are critically discussed in terms of the model of Seyden-Penne and coworkers.

Regioselective Carboxylation of Silicon-Stabilized Allylic Carbanions and the Synthetic Utility of 2-Silyl-3-butenoates

Abstract Carbanions of allylic dimethylphenylsilanes show remarkable regioselectivity toward both carboxylation with carbon dioxide and methylation with methyl iodide. Methylation of these compounds occurred preferentialy at α position, although allyltrimethylsilane and allyltriphenylsilane are known to give γ selectivity toward the same electrophiles. Moreover, their aluminum “ate” complexes react with carbon dioxide regioselectively at the a position irrespective of methyl substitution pattern of the allylic moieties. The α-carboxylated allylic silanes proved to be useful synthons of 3-(methoxycarbonyl)allyl anions after esterification.

ChemInform Abstract: The Influence of (Organo)Metallics "Metal Tuning" on Stereo‐ and Regiochemical Convergence in Reactions of Allylic Carbanions with Aldehydes.

AbstractDie Regio‐ und Stereoselektivität der Addition der Allylanionen (I) an die Aldehyde (II) in Abhängigkeit von Metallchloriden (III) wird untersucht.

The influence of (organo)metallics “metal-tuning” on stereo- and regio-chemical convergence in reactions of allylic carbanions with aldehydes

Although the reaction of heterosubstituted allylic carbanions ( 2) with aldehydes generally produces a mixture of the γ- and α-adducts ( 4 and 3), syn- 3 and anti- 3 can be prepared either exclusively or predominantly by the proper choice of the organometallic compound added.

Selective hydrogenation of dienes on copper-chromite catalysts III reaction mechanism and nature of the occluded hydrogen species

We reported previously that the selective hydrogenation of dienes on copper chromite involves the association of a cuprous ion in an octahedral environment and an occluded hydrogen species as the catalytic sites. In this work, the reaction mechanism of isoprene hydrogenation is studied using deuterium as a tracer atom. The deuterium location, as well as the selectivities observed in the hydrogenation of 1,3-pentadienes are consistent with the formation of allylic carbanions. Moreover, these results suggest that a hydridic nature of at least a part of the occluded hydrogen is required. According to Siegel's model, a general reaction scheme is proposed and similarities between the properties of the copper chromite and the cuprous ion in homogeneous catalysts are reported.

The diastereospecific aprotic conjugate addition reactions of allylic anions-mechanistic aspects.

A ten-membered cyclic “chair-chair” - or “ trans -decalyl”-like TS is proposed to account for the diastereospecific aprotic conjugate addition reactions of allylic carbanions bearing polar, charge-stabilizing groups.

Regional convergence in the reaction of heterosubstituted allylic carbanions via allylic aluminum and boron ate complexes

Regional convergence in the reaction of heterosubstituted allylic carbanions via allylic aluminum and boron ate complexes

Addition of amines to conjugated dienes catalyzed by solid base catalysts

Addition of amines to conjugated dienes to yield unsaturated amines was carried out over solid base catalysts such as MgO, CaO, SrO, La 2O 3, ThO 2, and ZrO 2. Dimethylamine, ethylamine, piperidine, aniline, and triethylamine were used as amines, and 1,3-butadiene, and 2-methyl-1,3-butadiene were used as dienes. From all the reactions examined, CaO exhibited the highest activity, while ZrO 2 was inactive. The activities of catalysts varied with the pretreatment temperature. For the addition of dimethylamine to 1,3-butadiene, the pretreatment temperatures which gave the maximum activities were 600 °C for CaO, 650 °C for La 2O 3, 700 °C for MgO(I) (prepared from Mg(OH) 2), and 500°C for MgO(II) (prepared from commercial MgO). The reactivities of amines are in the order: dimethylamine > ethylamine > piperidine ⪢ aniline, triethylamine. In the addition of dimethylamine to 1,3-butadiene, primary products consisted mainly of N,N-dimethyl 2-butenyl-amine which resulted from 1,4-addition of a dimethylamino group and an H to the diene for all catalysts. As the reaction proceeded, the 1,4-addition product underwent double-bond migration to the enamine over CaO, MgO(II), and SrO. The double-bond migration was slow over MgO(I), La 2O 3, and ThO 2. In particular, double-bond migration was not appreciable over La 2O 3. In the reaction of 2-methyl-1,3-butadiene with dimethylamine, N,N-dimethyl-3-methyl-2-butenylamine, which resulted from 4,1-addition of the amino group and an H, was produced as the main product for all catalysts except for MgO(I). Exchange of dimethylamine with D 2 was studied over CaO. Only one D atom was incorporated into dimethylamine, suggesting that amines dissociate into an H + and an amide ion on the catalyst surface. Based on these results, the reaction mechanisms were discussed, and it is proposed that addition of amines to conjugated dienes on basic catalysts proceeds via the amino allylic carbanion intermediates which result from addition of amide ions to the dienes.

ChemInform Abstract: GENERATION AND REACTIONS OF THE ALLYLIC CARBANION SPECIES FROM 2‐METHYL‐3‐(PHENYLTHIO)PROPENOIC ACID DERIVATIVES

AbstractDas aus der Z‐isomeren 3‐Phenylthio‐methacryl‐Säure (I) durch Umsetzung mit Lithium‐2,2,6,6‐tetramethylpiperidid (LTMP) in Tetrahydrofuran entstehende allylische Carbanion (II) reagiert mit Aldehyden und Ketonen (III) zu Hydroxycarbonsäuren (IV), die zur Isolierung lactonisiert werden.