The Witting Reaction

The Witting reaction has been investigated in aqueous conditions.305 Wittig olefination reactions with stabilized ylides (known as the Wittig-Homer or Homer-Wadsworth-Emmons reaction) are sometimes performed in an organic/water biphase system.306 Very often, a phase-transfer catalyst is used. Recently, the use of water alone as solvent... 

Bestmann, H. J., Vostrowsky, O. Selected Topics of the Witting Reaction in the Synthesis of Natural Products. 109, 85-163 (1983). 

A ketone or aldehyde is converted into an alkene by means of the Wit reaction. In this process, a phosphorus ylide, (also calledj... 

A special case is the use of the Witting reaction. Poly(p-phenylene pentadienylene)" ... 

A special case is the use of the Witting reaction. Poly(p-phenylene pentadienylene) [415] is prepared by this reaction first. This is utilized in a preparation of a block copolymer [456] according to the... 

Poly(phenyl vinylene) can be synthesized by several routes. One of them is step growth polymerization [80] by the Witting reaction ... 

The combination of solid-support and microwave irradiation directed towards the Witting reaction was investigated in the formation of 85. Multifuntionalized aldehyde 84 could be induced to react with solid-supported ylide 83 in a very efficient manner. 

The first example of a chiral phosphorous-atom ylide was communicated by Bestmann. The chiral reagent 93 underwent the Witting reaction with 92 to afford 94 but with poor chiral induction. 

Figure A3.14.2. Characteristic features of a clock reaction, illustrated for the Landolt reaction, showing (a) variation of product concentration witii induction period followed by sharp reaction event (b) variation of overall reaction rate witli course of reaction.

The subsequent reaction of tire F atoms witli tire silicon surface leads to tire fonnation of tire volatile product SiF ... 

These should be con describe the same reaction, s but at the limit of fine Physically the interesting f appearance of the pressure p ablej with the consequence describe the system at the at the limit of fine pores, true that the pressure wit ni sense that percentage variat of the pressure variations i permeability, so convective permeability and pressure gr the origin of the two terms... 

The C. 100-C. 101 diol group, protected as an acetonide, was stable to the Wit-tig reaction used to form the cis double bond at C.98-C.99, and to all the conditions used in the buildup of segment C.99-C. 115 to fully protected palytoxin carboxylic acid (Figure 1,1). 

Reaction of etio acid 67 with N,N-dimethylthioformamidoyl chloride probably gives initially the mixed anhydride 71 this is not isolated but undergoes O to S carbonyl migration to the anhydride 72. Saponification then leads to the thioacid 73. Reaction of the sodium salt of the acid witli bromochloromethane affords cloticasone propionate (74). The corresponding reaction with hioniofluoromethane leads to fluticasone propionate (75) [16]. 

Step 4 of Figure 27.7 Phosphorylation and Decarboxylation Three addition reactions are needed to convert mevalonate to isopentenyl diphosphate. Th first two are straightforward phosphorylations that occur by nucleophilic sul stitution reactions on the terminal phosphorus of ATP. Mevalonate is first cor verted to mevalonate 5-phosphate (phosphomevalonate) by reaction wit ATP in a process catalyzed by mevalonate kinase. Mevalonate 5-phosphat then reacts with a second ATP to give mevalonate 5-diphosphate (diphosphc mevalonate). The third reaction results in phosphorylation of the tertiar hydroxyi group, followed by decarboxylation and loss of phosphate ion. 

The various reactions are all elementary (witness the rate constants over the arrows) so the rates are... 

Quantitatively transfer the hydrolysis reaction solution to a 50-mL glass culture tube with a screw-cap by rinsing witli 3x5 mL of deionized water followed by 5 mL of 30% (v/v) sulfuric acid and one additional 5 mL of deionized water. Rinse the Teflon culture tube with acetone and transfer to the glass culture tube. Extract the acidic aqueous phase (pH 1) with 3 x 2.5 mL of toluene. Pass each upper toluene phase through approximately 3 g of anhydrous sodium sulfate contained in a 6-mL disposable filtration cartridge into a 10-mL volumetric flask. Adjust the volume of the solution to 10 mL with toluene. Condition a 3-mL diolsilane bonded silica gel SPE cartridge with two column volumes of toluene. Load a 5-mL aliquot of toluene solution and collect the eluate in a 125-mL round-bottom flask. Elute the column with an additional 50 mL of toluene (use the 75-mL reservoirs) and collect the eluate in the same round-bottom flask. Concentrate the toluene extract to approximately 3.0 mL at 40 °C under weak reduced pressure with a rotary evaporator. 

Four-membered rings. The study of the reaction between thiobenzophenone and methylenetriphenylphosphorane177 pointed out the presence of a reactive intermediate, thiaphosphetane, which decomposed either to a thiirane and triphenylphosphine or to the Witting alkene and a phosphine sulfide, depending on the temperature. 

The ability to analyze people can be especially important in dealing with hostile parties, such as key employees of your opponent. For example, in taking a deposition the good lawyer will be able to observe the witness closely and observe his reaction to the questions. The skilled lawyer can instinctively detect excessive nervousness which would characterize an area of examination disturbing to the witness. This signals the lawyer to bear down on this particular line of questioning and establish why the witness is so nervous. Pursuing the fine of inquiry may... 

Various isoforms of both HO and NOS can be expressed in recombinant systems. As a result, the immediate future will undoubtedly witness a wealth of mutagenesis experiments guided by the crystal structures. It also may be possible to trap in crystalline form the various intermediates of the HO reaction cycle, which will greatly facilitate a deeper understanding of the catalytic mechanism. Conformational dynamics appear to be quite important in HO, and hence, a variety of spectral probes such as NMR and fluorescence should prove especially useful in studying the role of protein dynamics in function. Overall there should be considerable optimism for understanding HO at the level of detail achieved for peroxidases and other well-studied enz5une systems. 

Even the nonverbal reactions of the interviewer can influence the witness. If, for example, the witness admits making an error in performing an operation and the interviewer shakes her head back and forth and lets out an exasperatedsigh, the interviewer has communicated her perception, what a stupid operator, without words. Thus an interviewer must remain constantly aware of the potential influence she can have on the witness. 

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