Synthesis of tri-substituted vinyl boronates via ruthenium-catalyzed olefin cross-metathesis

Tri-substituted vinyl pinacol boronates, which are key reactive intermediates in a variety of transformations, are synthesized using ruthenium-catalyzed olefin cross-metathesis of α-substituted vinyl boronates and various alkenes. Cross-metathesis of 2-isopropenyl pinacol boronate proceeds with moderate yield and high Z-selectivity when sterically unhindered cross partners are used. Cross-metathesis of vinyl boronates that possess α-substitution larger than a methyl group is also achieved. Yield and Z-selectivity are lower in these cases, and the success of a cross-metathesis reaction is highly dependent on the steric bulk surrounding the double bond of the α-substituted vinyl boronate.     

(E)-γ-Substituted Allylic Alcohols and α-Substituted Homoallylic Alcohols via Acidic Treatment of the Acetonides Derived from γ-Substituted Vinyl Diols

Treatment of the acetonides of γ-substituted vinyl diols under acidic deprotection conditions afforded γ-substituted allylic alcohols and α-substituted homoallylic alcohols.     

Sulfur-containing vinyl monomers. XIII. Cationic copolymerizations of vinyl sulfides with some vinyl monomers

Cationic copolymerizations of vinyl sulfides (VS) with some vinyl monomers with boron tri-fluoride-diethyl etherate catalyst were investigated to evaluate their monomer reactivities. The effects of VS on the copolymer yield and viscosity of the resulting copolymers revealed the inhibition or retardation mechanism which was explained in terms of the formation of a stable vinylsulfonium salt by the reaction between a propagating carbonium ion and VS monomer. From the results of copolymerizations of phenyl vinyl sulfide (PVS) with isobutyl vinyl ether (IBVE), β-chloroethyl vinyl ether (CEVE), α-methylstyrene (α-MeSt), and styrene (St), the relative reactivities of these monomers were found to be in the following order: IBVE > CEVE > PVS > α-MeSt > St. The relatively higher reactivity of PVS than St derivatives was explained on the basis of the conjugative and electron-donating nature of the VS monomer. The effects of alkyl and para-substituted phenyl groups in vinyl sulfides on their reactivities toward the propagating carbonium ion were correlated with polar factors and compared with those of the hydrolysis of α-mercaptomethyl chlorides. The transition state for the propagation reaction in cationic polymerization of VS was proposed to be a π-complex type structure.     

Stereoelective radical copolymerization of (RS)-α-methylbenzyl vinyl ether with (S)-(-)- or (R)-(+)-N-(α-methylbenzyl)maleimide

Racemic α-methylbenzyl vinyl ether was copolymerized with optically active (S)-(-)- or (R)-(+)-N-(α-methylbenzyl)maleimide using 2,2′-azobisisobutyronitrile in order to examine the possibility of stereoelective radical polymerization of vinyl-type racemic monomers. The resulting copolymers were found to have almost alternating sequences of the two kinds of monomeric units. The non-polymerized α-methylbenzyl vinyl ether, recovered from the copolymerization system, showed an optical activity of opposite sign to the optically active comonomer used, indicating clearly that the co-polymerization process is stereoelective. It was confirmed that α-methylbenzyl vinyl ether preferentially incorporated in the copolymer has the same absolute configuration as the optically active N-substituted maleimide.     

Application de reactions d'hydroalumination en synthese organique: obtention d'α-alkyl α-hydroxyesters par addition enantioselective de tetraalkylaluminates AU phenylglyoxalate de (−) menthyle.

Using tetraalkylaluminates prepared via hydroalumination in THF of various vinyl compounds resulted in selective addition to the keto group of phenylglyoxylic acid (?) menthyl ester. Not only simple alkyl groups but also functionalized alkyl groups were added. By this way, a variety of α-substituted mandelic acid (?) menthyl esters were obtained with diastereomeric excesses close to 70%.     

Rhodium-catalyzed synthesis of 2,3 – Disubstituted N-methoxy pyrroles and furans via [3+2] cycloaddition between metal carbenoids and activated olefins

For the first time, we report the synthesis of 2-substituted N-alkoxy pyrrole 3-carboxylate and furan 3-carboxylate via Rh-catalyzed [3+2] cycloaddition between α-diazo oxime ether or α-diazo carbonyl compounds with vinyl equivalents in a one-pot process. We have demonstrated ethyl vinyl ether as well as vinyl acetate as vinyl equivalents and both were found to give excellent yields. We have also demonstrated the synthesis of N-alkoxy dihydropyrrole derivatives by carrying out the reaction at low temperature.     

A stereoselective synthetic entry to β-substituted α-[(trans)-vinyl] phosphonamides

α-(trans-Vinyl) phosphonamides with different substituents at the β-position were stereoselectively synthesized in high yields by treatment of β-substituted α-epoxy-α-trimethylsilyl phosphines with oxidizing agents. The corresponding phosphonamides were unstable in most cases and underwent reductive elimination affording desilylated vinyl derivatives. In turn, α-epoxy phosphines resulted from the [1+2] addition of [bis(diisopropylamino)phosphino](trimethylsilyl)carbene 2 to aliphatic, aromatic, and heteroaromatic aldehydes. In this way, a great variety of vinyl compounds have been efficiently prepared through one-pot procedure.     

Inductive Charge Dispersal in Quinuclidinium Ions. Polar Effects,Part 13

Inductive charge dispersal to the α- β- and γ-positions of the solvated quinuclidinium ion has been examined by comparing the pK_a and the derived inductivities ρ_I of several 2- 3- and 4-substituted quinuclidinium perchlorates 4, 5 , and 6 , respectively. The same inductivity is observed at the practically equidistant β- and γ-positions. It, therefore, appears that polar substituent effects are transmitted directly through the molecule. As expected, inductivity is considerably higher at the α-positions where through-bond and direct induction coincide. The fact that the pK_a of all three series of salts correlate linearly with each other points to the common nature of these inductive electron displacements.     

γ-Amino vinyl sulfoxides in asymmetric synthesis. Synthesis of optically pure α-substituted β-amino nitriles

The synthesis of optically pure (E)- and (Z)-γ-amino vinyl sulfoxides derived from commercially available protected α-amino esters is reported. Hydrocyanation of the double bond with Et₂AlCN is completely stereoselective and provides enantiomerically pure α-substituted β-amino nitriles with complete control of the configuration at the α-carbon being exerted by the sulfinyl group.     

Die Acylierung von Acetylenen mit β, γ-ungesättigten Säurechloriden. Eine neue Synthese von 5-Cyclopentenonen

The Acylation of Acetylenes with β,γ-Unsaturated Acid Chlorides, A New Synthesis of 5-Substituted 2-Cyclopentenones The acylation of acetylenes with α,α-disubstituted, β,γ-unsaturated acid chlorides under Friedel-Crafts-type conditions leads to 5-substituted 2-cyclopentenones. Phenols are formed with β,γ-unsaturated acid chlorides bearing at least one α-H-atom. These transformations are explained by the intramolecular cyclization of the initially formed vinyl cation, which, in the cases of α,α-disubstituted acid chlorides, is followed by ring contraction. The reaction leading to 2-cyclopentenones is applied to the synthesis of some spiro[4.4]nona- and spiro[4.5]deca-2,6-dienones.     

Selenium heterocycles. XXX. Synthesis of 4-substituted vinyl 2-thioxo-1,3-dithioles and 5-substituted vinyl 2-thioxo-1,3-thiaselenoles

4-Substituted vinyl and 4-(4-phenyl-1,3-butadienyl)-1,2,3-thiadiazoles were prepared through the reaction of 4-aryl-3-buten-2-one semicarbazone and 6-phenyl-3,5-hexadien-2-one semicarbazone with thionyl chloride, respectively. Decomposition of these 1,2,3-thiadiazoles as well as the corresponding 1,2,3-selenadiazoles with base and subsequent addition of carbon disulfide afforded 4-substituted vinyl 2-thioxo-1,3-dithioles and 5-substituted vinyl 2-thioxo-1,3-thiaselenoles.     

Study of the enantioselectivity of the CAL-B-catalysed transesterification of α-substituted α-propylmethanols and α-substituted benzyl alcohols

A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different α-substituted α-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear or slightly branched groups are present. It is also found that ramification at the β-position of the L substituent has a deleterious effect on both lipase activity and enantioselectivity. Moreover, some α-substituted benzyl alcohols bearing medium-sized (M) substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good enantioselectivities (E=46–57) and similar reaction rates.     

E-2-benzylidenebenzocyclanones. II. IR and mass spectrometric investigations

A series of E-2-benzylideneindanones (a) -tetralones (b) and -benzosuberones (c) with OCH₃ (2–4), NO₂ (5–7) and F (8–10) substituents in ortho, meta or para position was studied by IR and mass spectrometry. The most important IR bands were assigned and stated correlations between some frequencies and the stereostructure or conjugation feature of the molecules investigated. IR spectra were also analyzed in order to find frequencies characteristic of the size of the alkanone ring. The mass spectrometric investigation aimed at determining fragmentation pathways and finding correlations between them and the ring size of the alkanone ring or the position of the substituents.     

Competitive thermal ene reaction and Diels-Alder reactions of 2-[N-(alk-2-enyl)benzylamino]-3-vinylpyrido[1,2-a]pyrimidin-4(4H)-ones

Thermal reaction of 2-[N-(alk-2-enyl)benzylamino]-3-(2-substituted and 2,2-disubstituted)vinylpyrido[1,2-a]pyrimidin-4(4H)-ones gave azepine, the desired ene products, and/or pyran derivatives. The formation of the latter was responsible for the [4+2] cycloaddition reaction between the α,β-unsaturated ester carbonyl moiety as a diene part and the alkenylamino moiety as an ene one. The reaction features depended upon the kinds of substituents both on the vinyl and alkenyl counterparts; strongly electron-withdrawing substituents on the vinyl moiety or an electron-donating substituent on the alkenyl one changed the reaction feature from the ene reaction to the hetero Diels-Alder reaction.     

A method of synthesis of phosphinic acids on the basis of hypophosphites: VII. Synthesis of pseudo-γ-aminobutanoyl peptides and other phosphinic analogs of γ-aminobutyric acid

A method of synthesis of pseudo-γ-aminobutanoyl peptides and other phosphinic analogs of γ-aminobutyric acid from hypophosphites is suggested. Silyl phosphonites formed by in situ addition of bis-(trimethylsilyl) hypophosphite to the corresponding α-substituted acrylates, styrene, or vinyl phosphonate used as unsaturated components in the synthesis react in situ with N-(ω-bromoalkyl)phthalimides by an Arbuzov reaction scheme, affording ω-(phthalimido)alkylphosphinic acids possessing β-substituted β-(alkoxycarbonyl)ethyl, β-phenylethyl, or β-(diethoxyphosphinoyl)ethyl substituents. Acid hydrolysis of these reaction products gives the target aminophosphinic acids: phosphinic analogs of γ-aminobutyric acid.     

Stereocontrolled fluorobenzylation of vinyl sulfones and α,β-unsaturated esters mediated by a remote sulfinyl group. Synthesis of functionalized enantiomerically pure benzylic fluorides

A sulfinyl group in an ortho position confers enough chemical and configurational stability to monofluorobenzylcarbanions to evolve in a completely stereoselective way in their reactions with β-substituted vinyl sulfones and α,β-unsaturated esters. Reactions afford easily separable mixtures of two epimers differing in the configuration of the center derived from the Michael acceptor (up to 98% de). They can be easily converted into enantiomerically pure γ-fluorinated γ-phenylsulfones and γ-phenylesters bearing two chiral centers.     

1,4-Conjugate addition of 2-hydroxynaphthazarins to acyclic and cyclic α,β-unsaturated ketones. Prototropic ring-chain tautomerism of the adducts

TsOH-Catalyzed reactions of 6,7-disubstituted 2-hydroxynaphthazarins and acyclic or cyclic α,β-enones afforded the corresponding Michael-type adducts, viz., 3-substituted naphthazarins in 17–78% yields. ¹H and ¹³C NMR and IR spectroscopy showed that the adducts with cyclohexenone and methyl vinyl ketone exist in CDCl₃ solutions as mixtures of open-chain and cyclic tautomers, whereas the adducts with cyclopentenones exist only as the open-chain forms.     

Carbon dioxide: A reagent for the protection of nucleophilic centers and the simultaneous activation of alternative locations to electrophilic attack: 15. A synthetic method for the α-substitution of N-phenylbenzylamine

N-Phenylbenzylamine has been converted into a variety of α-substituted derivatives in one-pot sequences, using carbon dioxide both for N-protection and α-carbon activation, and then subsequent lithiation at the α-carbon atom by either tert- or n-butyllithium. The resulting lithium carbamate reacts with electrophiles, followed smooth acid-catalyzed decarboxylation under mild condition to give α-substituted N-phenylbenzylamines in good yields.     

Cp*RuCl-Vinyl Carbenes: Two Faces and the Bifunctional Role in Catalytic Processes

Ruthenium vinyl carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-vinyl dihydrooxazines are preferentially obtained with the former, Z-vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η³-coordination mode of the ruthenium vinyl carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species.     

Pd-catalyzed ring opening of oxa- and azabicyclic alkenes with aryl and vinyl halides: efficient entry to 2-substituted 1,2-dihydro-1-naphthols and 2-substituted 1-naphthols

An efficient syntheses of 2-substituted 1,2-dihydro-1-naphthols and 2-substituted 1-naphthols has been developed that involves the sequential palladium-catalyzed ring opening of oxabicyclic alkenes with aryl and vinyl halides followed by oxidation of with IBX. In the first step of the sequence, a combination of Pd(OAc)2, PPh3, Zn, and PMP in dry DMF was employed to catalyze the ring opening of 7-oxabenzonorbornadienes with aryl and vinyl halides to afford the corresponding cis-2-substituted 1,2-dihydronaphthols in good to excellent yields. These reactions occurred under very mild conditions with a variety of aryl halides bearing electron-withdrawing or -donating groups. Similarly, a 7-azabenzonorbornadiene substituted with an electron-withdrawing group on the nitrogen atom underwent facile ring-opening reaction with aryl halides to provide cis-2-substituted (1,2-dihydro-1-naphthyl)carbamates in excellent yields. Oxidation of the intermediate 1,2-dihydro-1-naphthols using IBX yielded the corresponding 2-substituted 1-naphthols in good to excellent yields.