Dichloromethane solutions

C. Cyclobutanone (Note 16). The residue consisting of oxaspiro-pentane (35%) and dichloromethane (about 200 ml.) is added dropwise at room temperature to a magnetically stirred solution containing about 5-10 mg. of lithium iodide in 50 ml. of dichloromethane (Notes 17, 18), at such a rate as to maintain gentle reflux of the solvent. At the end of the addition when the reaction mixture returns to room temperature, the transformation into cyclobutanone is complete. The dichloromethane solution is washed with 20 ml. of saturated aqueous sodium thiosulfate and with 20 ml. of water. After drying over magnesium sulfate and concentration by distillation of the solvent through a 15-cm., helix-packed, vacuum-insulated column, the residual liquid consists of cyclobutanone (95%) and of 3-buten-2-one and 2-methylpropenal... 

Caution Addition of lithium iodide catalytic amount to a dichloromethane solution containing more than 30% oxaspiropentane leads to a very vigorous reaction. 

The drying process can be speeded up by dissolving the wet product in diohloromethane, removing the water layer in a separatory funnel, drying the dichloromethane solution over anhydrous magnesium sulfate, and removing the solvent on a rotary evaporator. 

Diaza-l 8-crown-6 has also been converted into polymeric materials by the reaction of 9 with toluenediisocyanate . The polymeric materials were prepared by stirring commercially available 9 with TDI in dichloromethane solution. Reaction was rapid and exothermic, but the mixture was not worked up until the next day. The product was a white solid which softened between 170—190° and decomposed between 250—270°. 

Methyliodobenzene difluoride cleaves aryl dithioketals. The reactions are conducted in dichloromethane solutions at 0 °C to give gem-difluoro compounds in 65-90% yields [4 (equation 6)... 

Solutions of the radical cations of 65b (R = H, Me, Ph) were conveniently generated by the addition of bromine to dichloromethane solutions of the correspondingTTDAF (93CC1226 94JOC2997). All radical cations exhibit similar spectra with g = 2.0071. In the case of R = H, Me, the signal con-... 

Tetramethyl-l,2-oxathietane (138) was prepared by diazotization of 139, which was prepared from the aziridine (140) (86JA3811).Tlie reaction presumably involves the decomposition of the sulfonium ion intermediate (141).Tire dichloromethane solution of 138 at -20°C is sufficiently stable to permit exploration of the chemical reactions. Tire oxathietane 138 undergoes a formal [[Pg.248]

Enantioselectivities were found to change sharply depending upon the reaction conditions including catalyst structure, reaction temperature, solvent, and additives. Some representative examples of such selectivity dependence are listed in Scheme 7.42. The thiol adduct was formed with 79% ee (81% yield) when the reaction was catalyzed by the J ,J -DBFOX/Ph aqua nickel(II) complex at room temperature in dichloromethane. Reactions using either the anhydrous complex or the aqua complex with MS 4 A gave a racemic adduct, however, indicating that the aqua complex should be more favored than the anhydrous complex in thiol conjugate additions. Slow addition of thiophenol to the dichloromethane solution of 3-crotonoyl-2-oxazolidinone was ineffective for enantioselectivity. Enantioselectivity was dramatically lowered and reversed to -17% ee in the reaction at -78 °C. A similar tendency was observed in the reactions in diethyl ether and THF. For example, a satisfactory enantioselectivity (80% ee) was observed in the reaction in THF at room temperature, while the selectivity almost disappeared (7% ee) at 0°C. 

The analytical capability of these matrices has been demonstrated for chiral amines [12, 13]. The procedure is illustrated in Fig. 8-4 for the separation of NapEtNH " CIO . Concentrated methanol/dichloromethane solutions of the racemic mixture were placed on a column containing the chiral macrocycle host. The enantiomers of the ammonium salts were resolved chromatographically with mixtures of methanol and dichloromethane as the mobile phase. The amounts of R and S salts in each fraction were determined by polarimetry. Because the chiral supported macrocycle interacts more strongly with S salts, the R salt passes through the column first and the S salt last, as seen in Fig. 8-4. 

Attempts to increase the yield of l//-l-benzazepines by carrying out the reactions under high nitrogen pressure were only marginally successful. For example, in dichloromethane solution and 10 kbar nitrogen pressure for seven days, the yield of dimethyl 1-methyl-l //-benzazepine-3,4-dicarboxylate is increased to only 20%.144... 

Chloro-l//-l-benzazepines 2 are obtained as unstable red oils in excellent yields by heating 1 //-l-benzazepin-2(3//)-ones 1 with phosphoryl chloride in pyridine.208 Reaction conditions are important since in the absence of pyridine, or in dichloromethane solution, only poor yields of dimers, e.g. 3, are produced. The chlorobcnzazepines are stable for only short periods (24 hours in anhydrous pyridine) and rapidly polymerize. Isolation of the pure chloro compounds is difficult since they undergo very rapid hydrolysis to the benzazepinones. 

Attempts to induce valence isomerization of 5W-dibcnz[c,e,]azepine (3) to dihydrophenanthro-[9,10-6]azirine under thermal conditions have failed.85 However, the aziridine 5 is formed, albeit in low yield (3 %), by irradiating the dibenzazepinc 3 in dichloromethane solution. Isomerization can also be achieved by deprotonation of SH-dibenzIr.eJazepine with lithium diiso-propylamide at — 78 "C, and then allowing the resulting anion 4 to reprotonate by heating the reaction mixture at 50°C.85... 

The addition of vinylmagnesium bromide to methyl (S)-3-benzyloxy-4-oxobutanoate (5) in tetrahydrofuran proceeded with a slight preference for the nonchelation-controlled reaction product (40 60)5°. A reversal of the diastereoselectivity (80 20) could be observed when the Grignard reagent, as a solution in tetrahydrofuran, was added to a dichloromethane solution of the aldehyde which had been precomplexed with one equivalent of magnesium bromide. The almost exclusive formation of the chelation-controlled reaction product 6 was achieved when tetrahydrofuran was completely substituted by dichloromethane the presence of tetrahydrofuran interferes with the formation of the chelate complex, which is a prerequisite for high chelation-controlled diastereoselection. 

In many instances, the dichloromethane solution can be dried adequately by a simple filtration through coarse filter paper. 

The checkers found it convenient to separate the aqueous phase from the sticky amorphous mass and then later dissolve the product in the dichloromethane solution that was used for the extractions,... 

Polymerization of 4-bromo-6,8-dioxabicyclo[3.2.1 ]octane 2 7 in dichloromethane solution at —78 °C with phosphorus pentafluoride as initiator gave a 60% yield of polymer having an inherent viscosity of 0.10 dl/g1. Although it is not described explicitly, the monomer used seems to be a mixture of the stereoisomers, 7 7a and 17b, in which the bromine atom is oriented trans and cis, respectively, to the five-membered ring of the bicyclic structure. Recently, the present authors found that pure 17b was very reluctant to polymerize under similar conditions. This is understandable in terms of a smaller enthalpy change from 17b to its polymer compared with that for 17a. In the monomeric states, 17b is less strained than 17a on account of the equatorial orientation of the bromine atom in the former, whereas in the polymeric states, the polymer from 17b is energetically less stable than that from 17a, because the former takes a conformation in which the bromine atom occupies the axial positioa Its flipped conformation would be even more unstable, because the stabilization by the anomeric effect is lost, in addition to the axial orientation of the methylene group. 

It was of interest to see if the use of tm-butyl hypobromite would provide similar opportunities for regioselectivity to those found in the case of chlorination reactions with te/t-butyl hypochlorite. The initial indications were favourable use of H zeolite X as catalyst in dichloromethane solution gave an almost quantitative yield of bromotoluenes with a para ortho ratio of 81 19 (Fig. 5) (ref. 10). 

The yellow dichloromethane solution turns colorless, and a precipitate of benzeneseleninic acid appears. 

With three sulfur atoms above and three below the equatorial plane of the molecule, 190 was expected to be a good ligand for metal ions. However, a dichloromethane solution of 190 did not extract any ions from an aqueous solutions of various metal salts (in total 23 different cations including AP+,Ba +,... 

Luminescence experiments in dichloromethane solution indicated that the fluorescence of the phenylacetylene branches is quenched, whereas intense emission is observed from the binaphthol core. This antenna effect represents the first example of efficient (>99%) energy migration in an optically pure dendrimer. The fluorescence quantum yield increases slightly with increasing generation the values of 0.30,0.32, and 0.40 were obtained, respectively, for 10-12. 

In dichloromethane solutions, excitation of the chromophoric groups of the dendrons causes singlet-singlet energy transfer processes that lead to the excitation of the porphyrin core. It was found that the dendrimer 17, which has a spherical morphology, exhibits a much higher energy transfer quantum yield (0.8) than the partially substituted species 13-16 (quantum yield <0.32). Fluo-... 

Elsevier and co-workers have found that complexes of the type 4 (Scheme 13.5) were surprisingly resistant to reductive elimination [30]. However, this behaviour is not inconsistent with previous observations the A -substituent on the NHC is the bulky mesitylene, and whilst bulky substituents do not prevent decomposition they restrict approach of the a>methyl group, resulting in less effective interaction between the methyl and the NHC [5, 19]. The authors did, however, find that addition of CO to a dichloromethane solution of the complex led to rapid decomposition (R = Me) via reductive elimination to give the 2-acylimidazolium salt 5. 

The effect of dinitrogen pentoxide in a dichloromethane solution on diethyl ether at a temperature lower than 20°C caused a detonation. It was explained by the decomposition of nitroglycol formed as follows ... 

Using the pseudo-first-order equation A obsd = 0 + co2 [COiKwhere kcoi is the second-order rate constant for the reaction of carbene with CO2 and ko is the rate of carbene decay in the absence of CO2), solution-phase values of kcoi for phenylchlorocarbenes 9 and 12, and diphenylcarbenes 14 and 15 in dichloromethane were estimated (Table 4.1). (The concentration of CO2 in saturated dichloromethane solution at 25°C and 1 atm is 196mmol/L. ) The trend of these estimated second-order order rate constants agrees with that observed in low-temperature matrices by Sander and co-workers. ... 

Parallel studies of extracts and mixtures of compounds isolated from ragweed, Ambrosia artemisiifolia L., were also made. Water extracts of ragweed proved highly inhibitory of seed germination. Mixed sesquiterpenes isolated from ragweed were very inhibitory of onion, oat, ryegrass, and Palmer amaranth germination when applied in a dichloromethane solution pretreatment. 

X-ray structural information on halide binding to neutral organic it-receptors is limited to a few recent reports [23,24,62,89-91 ]2. In fact, the slow diffusion of hexane into a dichloromethane solutions of tetracyanopyrazine containing the alkylammonium salts of either chloride, bromide or iodide affords yellow to red crystals with UV-Vis absorptions closely resembling the elec-... 

In a similar manner, the diffusion of hexane into dichloromethane solutions containing mixtures of the alkylammonium salts of bromide and the olefinic acceptors o-CA and TCNE result in the formation of brown-red crystals [23]. X-ray analysis reveals the (1 1) complex of bromide with o-CA, in which the anion is located over the center of the C - C bond of the acceptor moiety (Fig. 15b) and Br - C contacts are shortened by as much as 0.6 A relative to the sum of van der Waals radii (Table 3). In bromide complexes with TCNE, the location of the anion relative to the acceptor is variable. In fact, a 2 1 complex [(Br )2,TCNE] is isolated in which both anions reside over the olefinic bond when the tetraethylammonium salt of bromide is used. In comparison, if the tetrapropyl- or tetrabutylammonium salts of the same anion are employed, the (1 1) complexes [Br ,TCNE] are formed in which the bromide donors are shifted toward the cyano substituents (Fig. 15a). In both cases however, the short intermolecular separations that are characteris-... 

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