Chain Installation

FIG. 12-66 Kiln chain installation (patented). (Allis-Chalmers Coip.)... 

Asymmetric syrc-selective aldol reaction of four carbons enolates (with attached chiral auxiliary) 290 and acrolein equivalent 291 was the key step in the Pettus synthesis of KDO [153]. Condensation adduct 292 was converted into the hydroxy lactone 293, which in turn after silyl deprotection and diol side chain installation gave lactone 204. Final addition of a carboxylic acid to the lactone carbonyl group of 204 was done with a-ethoxy vinyllithium. Reductive ozonolysis of the surrogate provided the ethyl ester 138 (Scheme 62). 

The side chain is formally the assembly of an oxalate derivative, A-benzoylpiperazine and the azaindole (Figure 7). In exploring alternate options, we sought to explore both stepwise and convergent approaches—modifying the synthetic location of the side-chain installation and seeking an approach that offered the greatest impact to the overall efficiency of the synthesis. 

Route A Triazole coupling prior to the C3-acylation and prodrug installation. Leveraging the results described above, an Ullmann coupling on C7-bromide 105 would furnish 12—a known intermediate in the existing synthesis. We could then follow either of the previous approaches—elaboration with the C3-side-chain installation or alkylation with the thioether to arrive at API (Section I). 

Another common use of carbopalladation is to effect a net annelation by side chain installation followed by cyclization. One example from the synthesis of a protected form of the 2-quinolone portion of streptonigrin 40 begins with iodide 37 (Scheme Heck reaction of this electron-rich fully substituted aryl iodide 37 with methyl acrylate provides the substimtion product 38. Extended reflux of 38 under acidic conditions promotes double deprotection, isomerization, and cyclization reaction yielding enamide 39. Another example from the synthesis of ( )-aurantioclavine 41 involves coupling of aryl bromide Standard Heck conditions provide the substitution product 43 in excellent yield at the appropriate oxidation state for cyclization to form the azepine ring en route to the natural product... 

Piccionello and co-workers have also developed a versatile and efficient Boulton-Katritzky rearrangement involving a N-N-C side-chain. Installation of the side chain was effected by SNAr substitution with methylhydrazine and subsequent imine formation with 4-trifluoromethyl-benzaldehyde (19), to provide 20. Solvent free thermolysis gave 21 in nearly quantitative yield. 

Are swing gates or chains Installed at the top of ladders and/or on access platforms ... 

Figure 3.2 Concept for the local chain-installation of a discrete amount of an acceptor monomer during the living polymerization of a large excess of a donor monomer. The bottom part of the figure shows a simplified view of the chain-to-chain distribution of the acceptor comonomer in the final sample.

Chain installation. Inspect chain to make sure it is free from dirt or grit before it is installed. Fit the chain around both sprockets, bringing the free ends together on one sprocket as shown in Fig. 5.100. Insert connecting link and secure in place. 

As was noted earlier, offset sidebar chains wear differently than straight sidebar chains. Offset sidebar chains must be installed to run in a particular direction to obtain better wear life. This will be covered in the chapter on chain installation. 

An inspection program for each chain installation should be established and followed. A checklist of items to inspect should be made and a record of maintenance action kept. Trends can be tracked that way and the chain can be adjusted or replaced before a costly failure occurs. 

LUBRICATE THE CHAIN. Prop up the bike so that the back tire spins freely. With the chain installed on the bicycle, mark one link with a permanent marker so you know when you ve cycled through all the links. Place a small drop of chain lube at each chain junction, stopping when you cycle through to the marked link. Turn the pedals for a couple of minutes to work the lube in between the links. Then hold a rag loosely around the chain and turn the pedals to drive the chain through the rag a couple of times. Any lubricant left on the surface of the chain will trap dirt and grime. 

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