Tetrahedral mechanism synthetic reactions

TABLE 10.8 The More Important Synthetic Reactions of Chapter 10 that Take Place by the Tetrahedral Mechanism"... 

TABLE 10.8 The more important synthetic reactions of Chapter 10 that take place by the tetrahedral mechanism. Catalysts are not shown... 

Aluminum methoxide Al(OMe)3 is a solid which sublimes at 240 °C in vacuum. Aluminum isopropoxide melts in the range 120-140 °C to a viscous liquid which readily supercools. When first prepared, spectroscopic and X-ray evidence indicates a trimeric structure which slowly transforms to a tetramer in which the central Al is octahedrally coordinated and the three peripheral units are tetrahedral.162,153 Intramolecular exchange of terminal and bridging groups, which is rapid in the trimeric form, becomes very slow in the tetramer. There is MS and other evidence that the tetramer maintains its identity in the vapour phase.164 Al[OCH(CF3)2]3 is more volatile than Al[OCH(Me)2]3 and the vapour consists of monomers.165 Aluminum alkoxides, particularly Al(OPr )3, have useful catalytic applications in the synthetic chemistry of aldehydes, ketones and acetals, e.g. in the Tishchenko reaction of aldehydes, in Meerwein-Pondorf-Verley reduction and in Oppenauer oxidation. The mechanism is believed to involve hydride transfer between RjHCO ligands and coordinated R2C=0— A1 groups on the same Al atom.1... 

Acyl halides are so reactive that hydrolysis is easily carried out. ° In fact, most simple acyl halides must be stored under anhydrous conditions lest they react with water in the air. Consequently, water is usually a strong enough nucleophile for the reaction, though in difficult cases hydroxide ion may be required. The reaction is seldom synthetically useful, because acyl halides are normally prepared from acids. The reactivity order is F < Cl < Br < If a carboxylic acid is used as the nucleophile, an exchange may take place (see 16-79). The mechanism ° of hydrolysis can be either SnI or tetrahedral, the former occurring in highly polar solvents... 

Abstract The basics of stereoselective reactions and reaction stereochemistry—the relation of stereoselectivity to the topology of tetrahedral and planar units in organic molecules—are discussed. The kinetic control of enantioselective reactions and characteristics of enantioselective and diastereoslective reactions is presented. Asymmetric syntheses are exemplified by the hydrogenation of C=0 and C=NR bonds in prochiral substrates catalyzed by organometallic complexes with chiral phosphine ligands. The mechanism of asymmetric alkylation of stabilized carban-ions in specifically designed chiral substrates and the practicability of this mefliod in the preparation of optically pure a-alkyl carboxylic acids are discussed. The synthetic approach to chiral auxiliaries and importance of recycling are presented. 

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