Dichloromethane as solvent

The second important group of configuralionally stable bis-protected a-amino aldehydes are the V-dibenzvl derivatives 5, easily prepared from amino acids in a three-step procedure65. These aldehydes react with various nucleophiles to normally provide the nonchelation-con-trolled adducts in high diastereoselectivity. This anti selectivity is observed when diethyl ether or telrahydrofuran is used as reaction solvent. Certain Lewis acidic nucleophiles or additives, such as tin(IV) chloride, in dichloromethane as solvent force chelation and therefore provide the. syn-adducts, once again with a high diastereoselectivity. 

However an unexpected new cyclic ruthenium phosphorus ylide half-sandwich complex 42 has been obtained by reaction of 41 with dichloromethane as solvent [79]. The cyclisation involves a C-Cl activation and corresponds to the incorporation of the methylene moiety in the P-C bond and to the ortho-metal-lation of one phenyl of the phosphine. An other novel unusual phosphonium ylide ruthenium complex 43 has also recently been described [80]. 

However, the main stimulus for switching from chemical to enzymatic deacylation was to avoid the use of dichloromethane as solvent (Brugging et al, 1998). The enzymatic process acounts for most of the several thousands of tons of 6-APA produced annually on a worldwide basis. 

Diels-Alder cycloaddition of 5-bromo-2-pyrone with the electron-rich tert-butyldi-methylsilyl (TBS) enol ether of acetaldehyde, using superheated dichloromethane as solvent, has been investigated by Joullie and coworkers (Scheme 6.90) [188]. While the reaction in a sealed tube at 95 °C required 5 days to reach completion, the anticipated oxabicyclo[2.2.2]octenone core was obtained within 6 h by microwave irradiation at 100 °C. The endo adduct was obtained as the main product. Similar results and selectivities were also obtained with a more elaborate bis-olefin, although the desired product was obtained in diminished yield. Related cydoaddition reactions involving 2-pyrones have been discussed in Section 2.5.3 (see Scheme 2.4) [189]. 

The readily prepared immobilized phosphoramidite could be used to efficiently synthesize oligodeoxyribonucleotides with modified thymidine residues. Whereas the effect of microwave irradiation on the deprotection by exposing the strand to tet-rakis-triphenylphosphine palladium(O) and diethylammonium bicarbonate was only small using dichloromethane as solvent, complete removal of the alloc group was achieved in N,N-dimethylformamide within 10 min at 80 °C (Scheme 7.30). After the reaction, the solid-supported product was washed with N,N-dimethylformamide and dichloromethane and dried, before being subjected to acylation. The coupling... 

At Coventry we have electropolymerised styrene in the presence and absence of ultrasound (38 kHz) at 0°C and at two different currents (100 mA and 400 mA). We used bright platinum electrodes, dichloromethane as solvent and tetrabutyl ammonium boron hexafluoride (TBABF5) as the electrolyte. At 400 mA we obtained complete conversion in 150 min vhth a resultant molar mass of 100000 compared with 70% conversion and a molar mass of 314000 in the absence of ultrasound. 

To prevent dimerization the concentration is kept low (10 3mol/l) but lower concentrations are allowed, when required by the bad solubility of the precursor. As an oxidizing agent 5.0 mol-% iodine in an atmosphere of air is frequently used. To prevent oxidation of the endproduct sometimes deaeration of the solvent and use of 100 mol- % iodine may be a better choice. Other useful agents are k-acceptors like tetracyanoethylene (TCNE) in dichloromethane as solvent. In most cases the helicenes are well separated from the irradiation mixture by evaporating the solvent and chromatography of the residue. In cases where the separation of the helicene and cis-olefin is difficult it is of advantage to irradiate until the olefin has completely reacted. 

The complexes were prepared from [CODRhCl]2 and 1.1 equiv of chiral diphosphine in dichloromethane as solvent. The chiral complex was added to a suspension of the support in dichloromethane. After being stirred for 24 h, the solid was filtered, washed with dichloromethane until the solvent showed no color, and afterward dried at room temperature for 16 h. In order to remove the excess of Rh complex not fixed to the solid carrier, the catalysts were extracted with methanol in a Soxhlet apparatus under reflux for 24h (Scheme 2.1.6.1). Both ICP-AES analysis and FTIR spectra of the remaining solvent indicated no content of homogeneous complex. The resulting catalysts had a pale yellow color similar to that of the homogeneous complex. 

The nitrosyl complex [Rh(NO)(PPh3)3] (36) catalyzes the hydrogenation of both 1-hexene and cyclohexene in dichloromethane as solvent and was also found to add deuterium to cyclohexene without H/D scrambling.138 A further study extended the range of substrates hydrogenated to internal alkenes, to conjugated and non-conjugated dienes, activated alkenes and terminal and internal alkynes.139... 

Use of less reactive alkylating agents such as dialkylcuprates, R2Zn or R2Cd, as described above, is one way to overcome this problem, but the yields are variable. The use of dichloromethane as solvent at -78 C resulted in good yields of alkylation product (84-94%),28 and a more general solution is achieved... 

The formation of peracids as the effective oxidizing species has often been proposed for oxidations with sodium percarbonate in the presence of organic acids or acid anhydrides30-32. It was observed that at room temperature and in dichloromethane as solvent, the addition of acetic anhydride induced the epoxidation by sodium perborate of mono-, di- and trisubstituted alkenes, including a,/i-unsaturated ketones in a slightly exothermic reaction33 (equation 6). 

Reaction conditions 10mol% catalyst, 25° C. aIn dichloromethane as solvent. 

Studies of the reactions of quinoxaline N-oxides under Reissert reaction conditions have led to some very interesting and unusual results. Thus, treatment of quinoxaline IV-oxide with PhCOCl/KCN in methanol or water under standard Reissert conditions gave 6-chloroquinoxaline as the major product (ca. 45%), and only small amounts of the desired 2-cyanoquinoxaline. Use of 3 equivalents of TMSCN in place of KCN and dichloromethane as solvent, however, gave 2-cyanoquinoxaline in 72% yield. When 2,3-diphenylquinoxaline iV-oxide was treated with 1 equivalent of PhCOCl in the presence of 3 equivalents of either KCN or TMSCN a mixture of products was always obtained irrespective of the solvent used. The most interesting of these products was the ring cleaved compound 1. 

Enantiopure fused oxopiperazino-/3-lactams have been produced by application of the Staudinger reaction with 5,6-dihydropyrazin-2-(l/7)-ones and the /3-lactams were converted to the 2-oxopiperazine-3-acetic acid esters in good yield with no epimerization (Equation 86) <2006TL8911>. Fused /3-lactams have been formed from macrocyclic imines by use of the Staudinger reaction (see Section 2.04.9.7). When phenoxyacetyl chloride and triethylamine were used, the best yields (45-52%) of the fused /3-lactams were obtained with dry dichloromethane as solvent <2006TL8855>. 

With p-tolyldiazonium salts (4-MeC6H4N2 X"), in the presence of oxidiz-able anions like B(Ph)4 or oxalate or bromide, electron transfer quenching of the diazonium excited state gives aryl radical. Ion pairing, when forced by the use of dichloromethane as solvent, favours this process [227],... 

This methodology still suffers from the shortcomings of salt formation and the use of bromide (10 mol%) as a cocatalyst and dichloromethane as solvent. Recently, a recyclable oligomeric TEMPO derivative, PIPO, derived from a commercially available polymer additive (Chimasorb 944) was shown to be an effective catalyst for the oxidation of alcohols with NaOCl in the absence of bromide ion using neat substrate or in e.g. methyl tert-butyl ether (MTBE) as solvent (Fig. 1.21) [71]. 

Polymerisation of ethylene was also attempted in [C4Ciim][PF6] or [Cspy][Tf2N], employing the palladium compound 45 together with either Ag[SbF6] or Na[BARF] to activate the complex.1681 However, the best activity obtained in these ionic liquids was one order of magnitude lower compared to using dichloromethane as solvent. 

On the basis of these results, we have developed the first method for the enantiose-lective synthesis of chiral /3-amino acid esters from achiral imines and ketene silyl acetals using BLA 28. The enantioselectivity of the aldol-type reaction is dramatically increased by using sterically bulky A-substituents. Condensation of the imine derived from benzhydrylamine occurs with high enantioselectivity (90 % ee) (Eq. 80). Furthermore, the best result (96 % ee) is achieved by use of a 1 1 (v/v) mixture of toluene and dichloromethane as solvents. Thus, excellent enantioselectivity (95 % ee or better) has been achieved in reactions of aromatic aldehyde-derived imines... 

Compared to the older procedures the use of acid iodides in acetonitrile or dichloromethane as solvent constituted a remarkable improvement. Aromatic and aliphatic acyl cyanides are accessible by this route. For example acyl cyanides of cinnamic acid and phenylacetic acid could be obtained in 33% and 49% yields. Copper(I) cyanide in diethyl ether in the presence of lithium iodide gave a-cyano ketones in 50-70%. The reaction can be carried out at room temperature in diethyl ether or slightly above or at 80 C in acetonitrile. It is not possible to obtain the acyl cyanide from acryloyl chloride, chloroformate or oxalyl chloride by this approach. 

With normal-phase HPLC, oil samples were analyzed as is by simple dilution in n-hexane. A Du Pont Zorbax amino-bonded phase column, 25 cm x 0.46 cm ID, was used, with n-hexane and dichloromethane as solvents. For reversed-phase HPLC, Vydac 201TP5 columns were used (25 cm x 0.46 cm ID for analytical scale and 25 cm x 1 cm ID for preparative scale). Samples for reversed-phase HPLC were fractionated in order to remove the saturated hydrocarbons which can interfere with the separation mechanism. The samples dissolved in n-hexane were passed Baker silica solid-phase extraction cartridges. The PAH fraction was then collected by eluting with a 1 1 mixture of dichloromethane and methanol. Acetonitrile and dichloromethane were used in the HPLC gradient. 

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