Groups generators

Another indole/oxindole synthesis achieves the critical ortho-substitution by Sommelet-Hauser rearrangement of an anilinosiilfonium ion intermediate. Use of P-thioketones (G = R, an alkyl group) generates 2-substituted indoles, whereas P-thioesters (G = OR) lead to oxindoles. In each case, a 3-thio substituent must be removed by desulfuri2ation. 

This ion may then open up a new epoxy group generating another ion which can in turn react with a further epoxy group. 

For the nanotubes, then, the appropriate symmetries for an allowed band crossing are only present for the serpentine ([ , ]) and the sawtooth ([ ,0]) conformations, which will both have C point group symmetries that will allow band crossings, and with rotation groups generated by the operations equivalent by conformal mapping to the lattice translations Rj -t- R2 and Ri, respectively. However, examination of the graphene model shows that only the serpentine nanotubes will have states of the correct symmetry (i.e., different parities under the reflection operation) at the K point where the bands can cross. Consider the K point at (K — K2)/3. The serpentine case always sat-... 

Exchanging the position of the double bond and an electron lone pair in each grouping generates three resonance structures. 

Figure 3.3 Alkyl groups generated from straight-chain alkanes.

Q An electron pair from oxygen displaces the leaving Y group, generating a new carbonyl compound as product. 

Alpert has shown [47] that poly(succinimide)-silica can be further hydrolyzed to poly (aspartic acid)-silica or condensed with [3-alanine in aqueous solution to form a covalently bonded copolymer of 2-carboxyethyl aspartamide and aspartic acid. The content of carboxyl groups generated by this way has not been quantified directly, but the cation-exchange hemoglobin capacity has been measured for a series of the packings. Thus, the optimal concentration of poly(succinimide) used in the synthesis was found to be 2 5%. 

One 7i-bond of an aromatic ring can be converted to a cyclohexadiene 1,2-diol by reaction with enzymes associated with P. putida A variety of substituted aromatic compounds can be oxidized, including bromobenzene, chlorobenzene, " and toluene. In these latter cases, introduction of the hydroxyl groups generates a chiral molecule that can be used as a template for asymmetric syntheses. " ... 

EPDM backbone, together with the carbonyl and ether groups generated on the rubber itself causes the carbonyl and ether absorptions to increase. The absorption at 1630 cm of the fraw -vinylene bonds of TMPTA is mainly due to the grafting of TMPTA onto EPDM and partly due to the formation of vinylidene bonds at the chain ends on irradiation. The absorptions at 1460 and 1379 cm due to >CH2 scissoring vibration and —CH3 stretching vibration, respectively, result from the rubber and the grafted TMPTA. 

The penultimate example of macrocycles based on phenyl and acetylenic units has been the very recent report by Tobe [801 and Rubin [81] of cyclophane 134. Both groups generated 134 in the mass spectrometer by laser desorption of hexa-protected polyynes 135 (robust) and 136 (unstable), respectively (Scheme 31). 

The cyclization involves a nucleophilic attack of the malonic ester car-banion on the carbonyl carbon atom of the aldehyde, and the substituted malonic ester carbanion attacks the electron-deficient carbon atom bearing the iodine atom, or in the reverse order, to give 119. The hydroxyl group generated in the first step of the reaction attacks the carbon atom, giving the pyranose product. 

Fragmentation reactions can also be used to establish stereochemistry of acyclic systems based on stereochemical relationships built into cyclic reactants. In both the examples shown below, the aldehyde group generated by fragmentation was reduced in situ. 

The activation of DMSO toward the addition step can be accomplished by other electrophiles. All of these reagents are believed to form a sulfoxonium species by electrophilic attack at the sulfoxide oxygen. The addition of the alcohol and the departure of the sulfoxide oxygen as part of a leaving group generates an intermediate comparable to C in the carbodiimide mechanism. 

The condensation reactions occur only through the mediation of sylanol groups generated by hydrolysis. There are two main opportunities. The condensation can be carried out by oxolation or olation mechanisms. The oxolation occurs with the participation of two sylonol groups. In the course of the reaction a hydroxo ligand is exchanged for an oxo one [8] ... 

The benzotriazolyl derivative of acrolein acetal, compound 882, is lithiated, treated with chlorodiphenylphosphine, and the obtained intermediate is oxidized with hydrogen peroxide to phosphine oxide 883 (Scheme 145). The relatively acidic proton in derivative 883 is easily removed by a base, and the obtained anion adds to a carbonyl group of aldehyde or ketone. Subsequent rearrangement and elimination of the phosphorane group generates diene 884. For the derivatives of aldehydes (884, R2 = H), (E)-(E) stereoselectivity of the elimination is observed. Acidic alcoholysis of dienes 884 affords esters of P,y-unsaturated carboxylic acids 885 < 1997JOC4131>. 

Scheme 45 shows a general reaction of the pyrazole chemistry reported by Pinto et al. [88]. This group generated bis-pyrazoles (e.g., 171) from bis chromones (e.g., 172) and dibrominated bis-chalcones (e.g., 173) using similar reaction conditions as stated in Schemes 43 and 44. 

A magnesium enolate of 99 is susceptible to aldol condensation with 4-pentenal, and the crude product can be directly protected to give its ethyl carbonate 100. a-Hydroxylation of the carbonyl group yields the hydroxyl carbonate 101. Reduction of the carbonyl group generates a triol, and this compound can be simultaneously converted to carbonate 102. Swern oxidation of 102 gives ketone 103, which can be rearranged25 to produce lactone product 104 (Scheme 7-32). 

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