Workup

Then N-Boc-O-benzylserine is coupled to the free amino group with DCC. This concludes one cycle (N° -deprotection, neutralization, coupling) in solid-phase synthesis. All three steps can be driven to very high total yields (< 99.5%) since excesses of Boc-amino acids and DCC (about fourfold) in CHjClj can be used and since side-reactions which lead to soluble products do not lower the yield of condensation product. One side-reaction in DCC-promoted condensations leads to N-acylated ureas. These products will remain in solution and not reaa with the polymer-bound amine. At the end of the reaction time, the polymer is filtered off and washed. The times consumed for 99% completion of condensation vary from 5 min for small amino acids to several hours for a bulky amino acid, e.g. Boc-Ile, with other bulky amino acids on a resin. A new cycle can begin without any workup problems (R.B. Merrifield, 1969 B.W. Erickson, 1976 M. Bodanszky, 1976). 

This cleavage reaction is more often seen in structural analysis than in synthesis The substitution pattern around a dou ble bond is revealed by identifying the carbonyl containing compounds that make up the product Hydrolysis of the ozonide intermediate in the presence of zinc (reductive workup) permits aide hyde products to be isolated without further oxidation... 

Photooxidation of tetrafluoroethylene (TFE) and hexafluoropropylene (HEP) yield peroxides that can be decomposed to esters and ultimately long-chain ether-containing carboxyUc acids. Equation 6 shows a simplified version of what occurs during photooxidation and workup (TFE R = F,... 

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. 

Chemicals responsible for odor in some PUR foams were synthesised by polymerisation of PO in CH2CI2 with Bp2(C2H )20 catalyst (114). The yield was 25% volatile material and 75% polymeric material. The 25% fraction consisted of dimethyldioxane isomers, dioxolane isomers, DPG, TPG, crown ethers, tetramers, pentamers, etc, and 2-ethy1-4,7-dimethyl-1,3,6-trioxacane (acetal of DPG and propionaldehyde). The latter compound is mainly responsible for the musty odor found in some PUR foams. This material is not formed under basic conditions but probably arises during the workup when acidic clays are used for catalyst removal. 

In the laboratory, excess reagent in a product should be destroyed before workup. Addition of diluted aqueous ammonia is the most effective practice, if ammonia is otherwise acceptable. Combustibility is a minor problem. The open-cup flash point of 116°C for dimethyl sulfate is well above normal handling temperatures. Elammable, toxic vapors are given off at elevated temperatures. 

Workup of the complex reaction mixture was difficult and expensive. As a result, these surfactants have been withdrawn from the U.S. market. In Europe, Hoechst AG produces secondary alkanesulfonates by a similar reaction (eq. 12) ... 

Another synthesis of Lyral (51) consists of the reaction of myrcene with acrolein to give the myrac aldehyde [37677-14-8] (52). The aldehyde group, which is sensitive to acid hydration conditions with strong acids, has to be protected by formation of the morpholine enamine. The enamine is then hydrolyzed on workup after the acid-catalyzed hydration to produce Lyral (93—95). 

Manufacture of 2-acetylthiophenes involves direct reaction of thiophene or alkylthiophene with acetic anhydride or acetyl chloride. Preferred systems use acetic anhydride and have involved iodine or orthophosphoric acid as catalysts. The former catalyst leads to simpler workup, but has the disadvantage of leading to a higher level of 3-isomer in the product. Processes claiming very low levels of 3-isomer operate with catalysts that are proprietary, though levels of less than 0.5% are not easily attained. 

Hydrides. Zirconium hydride [7704-99-6] in powder form was produced by the reduction of zirconium oxide with calcium hydride in a bomb reactor. However, the workup was hazardous and many fires and explosions occurred when the calcium oxide was dissolved with hydrochloric acid to recover the hydride powder. With the ready availabiHty of zirconium metal via the KroU process, zirconium hydride can be obtained by exothermic absorption of hydrogen by pure zirconium, usually highly porous sponge. The heat of formation is 167.4 J / mol (40 kcal/mol) hydrogen absorbed. 

Methyl 2,4-DI-0-acelyl-3,6-dldeoxy-3-C-methyl-3-nliro-a-L-glucopyrannoslde (4). Methyl-o-L-rhamnopyrannoslde 3 (100 g, 0.55 mol) in water (1000 mL) was treated with Nal04 (200 g, 0 83 mol) at 20°C. After 3 h NaHCOa was added, the mixture poured into EtOH (4000 mL) and filtered The filtrate was concentrated atxl extracted with hot EtOH. The extract was cooled, filtered and treated with nilroethane (104 5 g, 1.4 mol) followed by a solution of Na (12 g, 0.52 at. g) In EtOH (750 mL). After 4 h at 20°C Ihe solution was treated with CO2, filtered and concentrated The mixture was treated with pyridine (400 mL) and AC2O (300 mL) at 20°C lor 12 h. Workup left a residue which dissolved In Et20 petroleum ether (1 1) (500 mL) and cooled afforded 36 g of 4 (19%), rryj 137-138"C, (alQ- O C (c 1). 

Methyl-4-lomiylcyclohex-2-ene-1-one (5). A mixture of 3 and methacrolein 4 in Ph was refluxed for 24 h. After workup 5 was obtained in 72% yield. 

One widely used method of formation of protected compounds involves polymer-supported reagents, with the advantage of simple workup by filtration and automated syntheses, especially of polypeptides. Polymer-supported reagents are used to protect a terminal — COOH group as a polymer-bound ester (RCOOR —( ) during peptide syntheses, to protect primary alcohols as... 

The main purpose of this filtration is to remove traces, if any, of palladium-containing compounds that might induce undesirable transformations, such as isomerization and polymerization, during the subsequent distillative workup. 

The submitters observed more precipitate on dilution with ether and recommended that the aqueous workup be performed In a hood. 

The precedent is strong for the involvement of oxetanes as Intermediates in carbonyl additions to pyrroles. " NMR evidence has been obtained far an oxetane adduct of acetone and N-methylpyrrole. The initial photoadduct was shown to rearrange readily on workup to the 3-(hydroxyalkyl)pyrrole derivative. 

The checkers found that unless the aqueous workup is cooled, the dichloromethane boils vigorously. 

An interesting feature of the synthesis is the use of allyl as a two-carbon extension unit. This has been used in the stereospecific synthesis of dicyclohexano-18-crown-6 (see Eq. 3.13) and by Cram for formation of an aldehyde unit (see Eq. 3.55). In the present case, mannitol bis-acetonide was converted into its allyl ether which was ozonized (reductive workup) to afford the bis-ethyleneoxy derivative. The latter two groups were tosylated and the derivative was allowed to react with its precursor to afford the chiral crown. The entire process is shown below in Eq. (3.59). 

While keeping the collected deuterioammonia at dry ice-isopropyl alcohol temperature, lithium wire (10 mg) is added, followed by a solution of 3/3-hydroxy-5a-cholest-7-en-6-one (161 50 mg) in anhydrous tetrahydrofuran (4 ml). The reaction mixture is stirred for 20 min, the cooling bath is then removed and the ammonia is allowed to boil under reflux for 40 min. A saturated solution of ammonium chloride in tetrahydrofuran is added dropwise until the deep blue color disappears and then the ammonia is allowed to evaporate. The residue is extracted with ether and the organic layer washed with dilute hydrochloric acid and sodium bicarbonate solution and then with water. Drying and evaporation of the solvent gives a semicrystalline residue which is dissolved in acetone and oxidized with 8 N chromic acid solution. After the usual workup the residue is dissolved in methanol containing sodium hydroxide (0.2 g) and heated under reflux for 1 hr to remove any deuterium introduced at C-5 or C-7. (For workup, see section II-B). 

In comparison with manganese dioxide, the DDQ reagent has several advantages for the oxidation of allylic alcohols. The quinone method is more reproducible only one equivalent of oxidant need be added and generally fewer side reactions are observed. On the other hand, the workup of DDQ reactions often requires chromatography and in the simpler cases lower isolated yields may be realized. 

S-compatible under special conditions, i.e., group deactivation, special procedure of workup, etc. -unknown or questionable compatibility... 

The oxidation of organic compounds by manganese dioxide has recently been reviewed. It is of limited application for the introduction of double bonds, but the advantages of mildness and simple workup make it attractive for some laboratory-scale transformations. Manganese dioxide is similar to chloranil in that it will oxidize A -3-ketones to A -dienones in refluxing benzene. Unfortunately, this reaction does not normally go to completion, and the separation of product from starting material is difficult. However, Sondheimer found that A -3-alcohols are converted into A -3-ketones, and in this instance separation is easier, but conversions are only 30%. (cf. Harrison s report that manganese dioxide in DMF or pyridine at room temperature very slowly converts A -3-alcohols to A -3-ketones.)... 

A solution of 17-cyanoandrosta-5,16-dien-3jS-ol acetate (46 g) and anhydrous potassium acetate (0.46 g) in methylene dichloride (310 ml) is treated with a mixture of 40% peracetic acid (37 ml) and anhydrous potassium acetate (1.84 g) in methylene dichloride (46 ml), the temperature of the solution being maintained below 25°. The mixture is stored at room temperature for 4 hr and then washed successively with water, 5% sodium bicarbonate solution (aqueous sodium bisulfite, 10g/150g water, has been used to decompose excess reagent before workup) and water until neutral. Evaporation of the dried solution and addition of ether gives 24.1 g of 5oc,6a-epoxy-17-cyanoandrost-16-en-3 -ol acetate mp 187-190°. One recrystallization from methanol gives 20.4 g of oxirane melting at 191-194°. 

The workup is accomplished simply by dilution with water and extraction with ether. Alternately, the reaction mixture can be neutralized with acetic acid before dilution with water, etc. 

Selectivity between A -olefins and other double bonds can often be excellent S-keto-A, A and A systems are relativelyunreactive, and functional groups at C-21 e.g., OH, OAc) or at C-20 e.g., CN, Br) normally do not interfere. With functional groups at C-20, the final products are 20-ketones rather than 20-aIcohols, the intermediate bromohydrin or cyanohydrin cleaving during workup to the ketone. 

To overcome this, the A -acetyl group is reduced with lithium aluminum hydride. The resulting basic enamine then reacts extremely rapidly and selectively with peracid. The derived epoxide is hydrolyzed very easily with alkali during the workup. 

Benzylenol ethers rearrange in an apparently similar fashion via photolytic fission of the benzyl-oxygen bond and subsequent recombination steps. Irradiation in quartz of a cyclohexane solution of 3-benzyloxycholesta-3,5-diene (250) leads to 23% (251), 13% (252) [presumably formed from (251) during workup] and 10% (253). ... 

Irradiation of a benzene solution of (267) containing a sixfold excess of l-acetoxybut-l-en-3-one leads to the formation of the two cyclobutane adducts [(278) 47% yield of converted starting material] and [(279) 20% yield], and the acetylcyclobutene [(280) 9 % yield]. The mode of formation of the product (280) is not yet established unambiguously, although it is not formed during workup. 

Alternatively, treatment of the monodibromocarbene adduct (48 0.7 g) with silver perchlorate (1.4 g) in refluxing 20% aqueous acetone (30 ml) for 30 min followed by the workup described above affords A-homo-estra-l,4,5(10)-triene-3,17-dione (50) in nearly quantitative yield. 

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