Stereoelectronic control in the base catalyzed hydrolysis of five-membered ring cyclic phosphonamidates

The base catalyzed hydrolysis of 2-phenyl-2-oxo-3-(2,6-dimethylphenyl)-1,3,2-oxazaphospholidine, $\text{6}$, and 2-phenyl-2-oxo-3-(2,6-diisopropylphenyl)-1,3,2-oxazaphospholidine, $\text{7}$, yields ring opened products involving 95% and 100% P-O cleavage, respectively.     

Stereoelectronic control of exo/endo rate ratios in the solvolysis of 2-norbornyl p-toluenesulfonates

The variable exo/endo rate ratios observed in the solvolysis of 6-exo-substituted exo- and endo-2-norbornyl p-toluenesulfonates are due to differential transmission of polar effects in the transition state for ionization.     

Determination of the rate constant for ring opening of an alpha-cyclopropylvinyl radical

The rate constant for ring opening of the 1-(trans-2-phenylcyclopropyl)ethen-1-yl radical, 4, generated by photolysis of the corresponding vinyl iodide 2, is reported. The value of the rate constant was determined by the tin hydride method and was found to be (1.6+/-0.2)x10(10) s-1, one order of magnitude smaller than the rate constant for rearrangement of the trans-2-phenylcyclopropylcarbinyl radical.     

Stereoelectronic control in regioselective carbohydrate protection

Organotin-mediated regioselective protection has been extensively used in organic synthesis for many years. However, the mechanistic origin of the resulting regioselectivity is still not clear. By the comparison of the steric and stereoelectronic effects controlling the geometry of five-membered rings formed from neighboring group participation, from intramolecular acyl group migration, or from orthoester transesterification on pyranoside rings, a theory on the pattern resulting from the reaction with dibutyltin oxide is presented. It is thus suggested that the regioselectivity of organotin-mediated protection is controlled by analogous steric and stereoelectronic effects as in neighboring group participation and acyl group migration, mainly dependent on the stereoelectronic effects of the pyranoside itself, and not related to complex stannylene structures. An organotin protection mechanism is also suggested, emanating from steric and stereoelectronic effects, nucleophilicity, and organotin acyl migration.     

Stereoelectronic effects in the ring cleavage of methyl glycopyranosides using dimethylboron bromide

Treatment of methyl D-glycopyranosides with dimethylboron bromide followed by a nucleophile gives acyclic products resulting from selective cleavage of the ring carbon-oxygen bond. The results are rationalized based on stereoelectronic considerations.     

Stereoelectronic control in the oxidation of gem-disulphides

The first example of stereospecific oxidation in the gem-disulphide series is reported; chemical, spectral, and X-ray evidence indicated the stereoelectronic discrimination between two modes of approach of electrophile in the conversion to meso-2,2-bis(methylsulphinyl)-1,3-diphenylpropane ($\text{2}$).     

The influence of α-trialkylsilyloxy groups on the rate of ring opening of cyclopropylmethyl radicals

The rate of ring opening of α-trialkylsilyloxycyclopropylmethyl radicals is about ten times slower than of the cyclopropylmethyl radical at 298K.     

Regioselectivity in the ring opening of non-activated aziridines

In this critical review, the ring opening of non-activated 2-substituted aziridines via intermediate aziridinium salts will be dealt with. Emphasis will be put on the relationship between the observed regioselectivity and inherent structural features such as the nature of the C2 aziridine substituent and the nature of the electrophile and the nucleophile. This overview should allow chemists to gain insight into the factors governing the regioselectivity in aziridinium ring openings (81 references).     

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.     

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.     

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.     

Furan ring opening—indole ring closure: pseudooxidative furan ring opening in the synthesis of indoles

A new approach to the synthesis of 4-(2-indolyl)-3-buten-2-ones is described based on condensation of 2-tosylaminobenzyl alcohols with N-tosylfurfurylamine. Pseudooxidative furan ring opening occurred via protolytic elimination of tosylamide from the side chain of the 2-tosylaminoaryl(5-tosylaminomethylfur-2-yl)methanes formed in situ.     

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.