Novel ring opening polymerization induced by alkali metal anions

Novel homogeneous initiation systems consisting of organic alkali metal complexes: Me⁺/Ligand, Me⁻ enable synthesis of “living” tailor made polymers and copolymers promising materials for engineering and biomedical applications. The mechanism of this polymerization has been elucidated.     

Trimethylchlorosilane induced ring opening of 2-alkyloxazolidines to enamine derivatives

2-Alkyloxazolidines (5) were ring-opened by trimethylchlorosilane with N,N-diisopropylamine to give N-[2-(trimethylsilyloxy)alkyll-enamines (6). A MgCl₂ promoted Michael reaction of chiral enamines thus prepared was achieved with asymmetric induction.     

Carbenoid type base induced ring expansion of the adducts of cyclic ketones with bis(phenylthio)methyllithium

In another application of the principle that metallo derivatives of bis(phenylthio)acetals behave as carbenoids when present in the same molecule with another anionic group, the adducts of cyclic ketones with bis(phenylthio)methyllithium react with an alkyllithium to yield the ring expanded α-(phenylthio) ketones.     

UV‐induced crosslinking of ring opening metathesis block copolymer micelles

Statistical and amphiphilic block copolymers bearing cinnamoyl groups were prepared by ring opening metathesis polymerization (ROMP). The UV‐induced [2 + 2] cycloaddition reaction of polymer bound cinnamic acid groups was studied in polymer thin films as well as in block copolymer micelles. In both cases, exposure to UV‐light for 10 min led to a crosslinking conversion of about 60%, as determined by FT‐IR spectroscopy and UV–vis absorption measurements. Time based IR‐spectroscopy revealed a maximum conversion of 78% reached after an irradiation time of about 16 min. For micelles obtained from polymers bearing 5 mol % or more cinnamoyl groups, the crosslinking reaction proceeded smoothly, yielding in crosslinked particles which were stable in a non‐selective solvent (CHCl₃). Diameters determined by dynamic light scattering in the selective solvent (MeOH) were similar for both, non‐crosslinked and crosslinked micelles, whereas diameters of crosslinked micelles in the non‐selective solvent (CHCl₃) were significantly larger compared to MeOH samples. This strategy of direct self assembly of block‐copolymers in a selective solvent followed by “clean” crosslinking, without the need for additional crosslinking reagents or crosslinking initiators, provides a straight forward approach toward ROMP‐based polymeric nano‐particles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2402–2413, 2008     

Palladium-mediated ring opening of hydroxycyclopropanes

[reaction: see text] The palladium-mediated ring opening of substituted cyclopropanols has been found to take place predominantly at the less substituted C-C bond. Thus, sequential application of the titanium-mediated cyclopropanation of esters and the palladium-mediated ring opening of the resulting cyclopropanols provides a convenient method for functionalizing monosubstituted olefins.     

Photochemical ring opening of barbital

Photolysis of barbital yields derivatives of urea and biuret. The mechanism of ring opening involves an isocyanate intermediate.     

Chemoselective ring opening of benzoxazaphosphinines

Cyclization of 2-[(4-chloroanilino)methyl]phenol (1) with thiophosphoryl chloride afforded 2-chloro-3-(4-chlorophenyl)-3,4-dihydro-2H-1,3,2λ⁵-benzoxazaphosphinine-2-thione (2). Reaction of 2 with various heterocyclic amines (3) in the presence of Et₃N/NaH gave 3-(4-chlorophenyl)-2-nitrogen heterocyclic substituted-3,4-dihydro-2H-1,3,2λ⁵-benzoxaza-phosphinine-2-thiones (4). Further reaction of 4 with the N-sodium salt of amino heterocyclics in the presence of HCl at 50-60 °C opened the benzoxazaphosphinine ring chemoselectively at the endocyclic P-O bond and yielded 2-[4-chloro(heterocyclic substituted-phosphorothioyl)anilino]methylphenols 5-13.     

Thermally induced skeletal inversion and ring opening of hexamethylbicyclo[2.2.0]hexanes

Hexamethylbicyclo[2.2.0]hexanes underwent endo,exo isomerization (skeletal inversion) and stereoselective supra, antara cleavage at 140–250°. The kinetics were studied and the products isolated and identified. The reactions are discussed in terms of a common 1,4-π-bonded intermediate which evolves to the invertomer or opens conrotatorially to methyl-substituted hexadienes.     

Scope of palladium-catalyzed alkylative ring opening

We have explored the scope of the palladium-catalyzed nucleophilic ring opening methodology. New highly selective and highly active catalysts have been found for the ring opening of oxabenzonorbornadienes. Employing these catalysts, the addition of various alkyl nucleophiles to oxabenzonorbornadiene has been achieved. In addition, reaction of diethylzinc with [3.2.1] oxabicyclic alkenes has been accomplished to yield ring-opened products as well as functionalized alkene addition products.     

Reductive ring opening reactions of diphenyldihydrofullerenylpyrroles

The reductive ring opening reaction conditions for the simple [60]fullerenyldihydropyrrole 1 have been optimized to include acetic acid in the reaction mixture to rapidly protonate the anionic intermediate. Under these conditions, the ring opened dihydrofullerene 2 was obtained in 68% yield. Under slightly modified conditions and at −78 °C, the reductive bis-ring opening of the tethered trans-4 isomer 3 provided the novel racemic bis-dihydrofullerenyl derivative 7.     

Cationic ring opening of functionalized diphosphiranes

The functionalized diphosphiranes 1 a–c, in presence of Lewis acid, undergo two kinds of reaction:the ring opening leading to the phosphenium-phosphonium ion 2a–c obtained according to an electrocyclic reaction and the fragmentation giving phosphaalkene 3a–c and phosphonium ion 4. The deprotonation reaction of 2a–c in hexane leads to phosphino-phosphaalkenes 6a–c.     

Unexplored nucleophilic ring opening of aziridines

The reactivity of dianions of carboxylic acids towards aziridines has been studied. Although, a similar reactivity to that of enolates from ketones, esters or amides has been observed, the method directly yields γ-aminoacids in one step. The method is complementary of previous results of enenediolate reactivity with other electrophiles. A comparative study with the reactivity of this enediolates with epoxides is included.     

Intramolecular guanidine epoxide ring opening reactions

The synthesis of a range of cyclic guanidines via intramolecular ring opening of epoxides or iodocyclisation is reported. A preliminary investigation of the glycosidase inhibitory activity of these substances is also discussed.     

Electrochemical oxidative ring opening of 1-methylcyclobutanol

The manganese(III) acetate-mediated electrooxidative ring opening of 1-methylcyclobutanol (1) in acetic acid affords pentane-2-one (2) as the major product. The reaction of 1-methylcyclobutanol with Mn(OAc)₃-LiCl gives 5-chloropentane-2-one (4.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1306–1307, May, 1996     

Quantum-chemical study of opening the ethylenimine ring

Conclusions We used the model reaction of opening the protonated ethylenimine ring by ethylamine for a quantum-chemical study of chain growth in the synthesis of linear polyethylenimine. Using the MPNDO/3 approximation we calculated the potential curve and found the transition state of this reaction. We obtained a good agreement of the calculated E_act and heat effect of the reaction with the experimental data on the polymerization of ethylenimine in inert nonpolar solvents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 442–445, February, 1984The authors express their gratitude to M. V. Bazilevskii for valuable consultations and to V. I. Faustov for graciously supplying the MPNDO/3 program.     

Regioselective epoxide ring opening. Steroselective synthesis of a tetrahydropyran ring

The stereoselective synthesis of a 2-substituted tetrahydropyran with adjacent alkoxy-bearing stereogenic centre is described. The key steps of this synthesis were the stereoselective epoxidation of an allylic alcohol and the regioselective epoxide ring opening by lithium aluminum hydride. The regio and stereoselective synthesis of a trihydroxyselenide and a trihydroxysulfide is also described. The latter compounds are not suitable for cyclization to tetrahydrofuran ring.     

Regioselective ring opening of alkylidenecyclopropanone silyl acetals

Alkylidenecyclopropanone silyl acetals are readily available from the reaction of an alkylidenemethyliodonium salt and ketene silyl acetals in the presence of triethylamine. The three different C-C bonds of the cyclopropane ring can be selectively cleaved with HCl, Lewis acid, or fluoride. The alkylideneallyl cation formed via the cleavage of C2-C3 bond with Lewis acids shows further selectivity in reacting with a nucleophile.