Dichloromethane, formation

When the pyrone 297 was exposed to base in dichloromethane, formation of the oxidopyrylium occurs and subsequent cycloaddition transpires. Lee found that when the allene tether was 3 (n = 0), cycloaddition occurs to form the bicy-clo[5.3.0]decadiene 298 exclusively, rather than the alternative bicyclo[5.2.0] nonadiene product 299. Increasing the tether length by one resulted in formation of the exo-substituted double bond (299) in 45% yield. Increasing the tether length by one carbon, to four, completely retarded the cycloaddition (Scheme 4.83). 

Recently Desimoni et used the same bis(oxazoline) ligand in the magnesium(II) catalysed Diels-Alder reaction of the N-acyloxazolidinone depicted in Scheme 3.4. In dichloromethane a modest preference was observed for the formation of the S-enantiomer. Interestingly, upon addition of two equivalents of water, the R-enantiomer was obtained in excess. This remarkable observation was interpreted in terms of a change from tetrahedral to octahedral coordination upon the introduction of the strongly coordinating water molecules. 

Fn some cases, r-allylpalladium complex formation by retention syn attack) has been observed. The reaction of the cyclic allyiic chloride 33 with Pd(0) affords the 7r-allylpalladium chlorides 34 and 35 by retention or inversion depending on the solvents and Pd species. For example, retention is observed in benzene, THF, or dichloromethane with Pd2(dba)3. However, the complex formation proceeds by inversion in these solvents with Pd(Ph3P)4, whereas in MeCN and DMSO it is always inversion[33]. The syn attack in this case may be due to coordination of Pd to chlorine in 33, because Pd is halophilic. The definite syn attack in complex formation has been observed using stereoche-mically biased substrates. The reaction of the cxoallylic diphenylphosphino-acetate 36 with phenylzinc proceeds smoothly to give 37. The reaction can be explained by complex formation by a syn mechanism[31]. However, these syn attacks are exceptional, and normally anti attack dominates. 

Write equations for the initiation and propagation steps for the formation of dichloromethane by free radical chlorination of chloromethane... 

From their structures, it appears that the hydrolytic stability of macrocyclic lactones must necessarily be inferior to macrocyclic polyethers. Ease of synthesis of the cyclic esters is therefore one of the aspects which commend them to interest. It is probably for this reason that such lactones have not been made more often by the interesting approach of Kdgel and Schroder . These workers report the ozonolysis of dibenzo-18-crown-6 in a mixture of methanol and dichloromethane at —20°. Reduction of the ozon-ide at —75° using dimethylsulfide followed by warming and addition of acetone led to formation of 6 in 14% yield. The bis-oxalate had mp 164—165° from acetone, very similar to that of the starting crown. The transformation is illustrated below in Eq. (5.9). 

The complexation procedure included addition of an equimolar amount of R,R-DBFOX/Ph to a suspension of a metal salt in dichloromethane. A clear solution resulted after stirring for a few hours at room temperature, indicating that formation of the complex was complete. The resulting solution containing the catalyst complex was used to promote asymmetric Diels-Alder reactions between cyclopen-tadiene and 3-acryloyl-2-oxazolidinone. Both the catalytic activity of the catalysts and levels of chirality induction were evaluated on the basis of the enantio-selectivities observed for the endo cycloadduct. 

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

If the alkyl halide contains more than one, equally reactive C-halogen centers, these will generally react each with one aromatic substrate molecule. For example dichloromethane reacts with benzene to give diphenylmethane, and chloroform will give triphenylmethane. The reaction of tetrachloromethane with benzene however stops with the formation of triphenyl chloromethane 7 (trityl chloride), because further reaction is sterically hindered ... 

Poloxamers are used primarily in aqueous solution and may be quantified in the aqueous phase by the use of compleximetric methods. However, a major limitation is that these techniques are essentially only capable of quantifying alkylene oxide groups and are by no means selective for poloxamers. The basis of these methods is the formation of a complex between a metal ion and the oxygen atoms that form the ether linkages. Reaction of this complex with an anion leads to the formation of a salt that, after precipitation or extraction, may be used for quantitation. A method reported to be rapid, simple, and consistently reproducible [18] involves a two-phase titration, which eliminates interferences from anionic surfactants. The poloxamer is complexed with potassium ions in an alkaline aqueous solution and extracted into dichloromethane as an ion pair with the titrant, tet-rakis (4-fluorophenyl) borate. The end point is defined by a color change resulting from the complexation of the indicator, Victoria Blue B, with excess titrant. The Wickbold [19] method, widely used to determine nonionic surfactants, has been applied to poloxamer type surfactants 120]. Essentially the method involves the formation in the presence of barium ions of a complex be-... 

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. 

Formation of a vinyl-substituted pyrrolizidine derivative is also observed in case of an allylstan-nane cyclization94. Since the allylstannane moiety is acid sensitive, the iV-acyliminium ion is generated by exposure of the hydroxylactam to methanesulfonyl chloride and triethylamine in dichloromethane. The very rapid cyclization produces the endo-vinyl compound with very high stereoselectivity. 

An example of the efficient formation of an electron-deficient double bond by RCM was disclosed by a Japanese group in a novel total synthesis of the macrosphelides A (209) and B (208) (Scheme 41) [100]. When the PMB-pro-tected compound 204 was examined as a metathesis substrate, the ring closure did not proceed at all in dichloromethane using catalysts A or C. When the reaction was carried out using equimolar amounts of catalyst C in refluxing 1,2-dichloroethane, the cyclized product 205 was obtained in 65% yield after 5 days. On the other hand, the free allylic alcohol 206 reacted smoothly at room temperature leading to the desired macrocycle 207 in improved yield. 

Efficient stirring is required. A solution of 225 g. (5.6 moles) of sodium hydroxide in 225 ml. of water can be added to the stirred mixture of the organic substrates in dichloromethane if a more efficient mechanical stirrer is used. In the original procedure, the submitters noted an induction period of about 20 minutes which was stated to vary somewhat with the stirring rate, stirring-bar size, and relative amount of phase-transfer catalyst. Three moles of base are required for the reaction one to generate the carbene and two to react with the additional two moles of hydrochloric acid lost by the amine-carbene adduct in the isonitrile formation step. If less base is used, the excess hydrochloric acid reacts with the isonitrile by a-addition, and the yield is substantially reduced. 

The formation of the acyl azide may be followed by the growth of the 2130-cm. (—N=N=N) infrared absorption of concentrated dichloromethane extracts of aliquots removed from the reaction. 

Catalytic incineration has been appHed in the abatement of chlorinated VOC emissions in the pharmaceutical industry. The major compounds in the emission mixture are dichloromethane, perchloroethylene, dimethylformamide, oxitol, and toluene. The incinerator operates normally at 400-500 °C, but when emissions contain perchloroethylene the temperature is increased up to 500-600 °C. The emission mixture also contains water, which pushes the selectivity further toward HCl formation instead of formation of CI2. After oxidation, the product gases are washed with NaOH scrubbers. The purification level of over 99% can be achieved with the incinerator, the activity of which has been shown to be very stable after one year of continuous operation [69-71]. 

To visualize bond formation by an outer atom other than hydrogen, recall the bond formation in HF. One valence p orbital from the fluorine atom overlaps strongly with the hydrogen 1 S orbital to form the bond. We can describe bond formation for any outer atom except H through overlap of one of its valence p orbitals with the appropriate hybrid orbital of the inner atom. An example is dichloromethane, CH2 CI2, which appears in Figure 10-11. We describe the C—H bonds by 5 -I S overlap, and we describe the C—Cl bonds by 5 - 3 p... 

The addition of a further equivalent of neutral ligand to a suspension of [ AuAg (C6F5)2L J in dichloromethane leads to a colorless solution which upon addition of n-hexane precipitates complexesof the type [AgLL ][Au(C6F5)2] with L = Py, L = py or L = phen, bipy, L = PPh3. Taking into account all available data, the probable formation of these complexes is shown in the Equation 3.11 ... 

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