Aryl-oxygen bond formation

You learned in Section 17 8 of the relationship among hemiacetals ketones and alcohols the for mation of phenol and acetone is simply an example of hemiacetal hydrolysis The formation of the hemiacetal intermediate is a key step in the synthetic procedure it is the step in which the aryl—oxygen bond is generated Can you suggest a reasonable mechanism for this step" ... 

The carbon-oxygen bond formation follows the same pathway. For both nitrogen-carbon and oxygen-carbon bond formation, a competing reaction is 13-hydride elimination (if a hydride is present at the heteroatom fragment), which lowers the yield and the reduced arene is obtained after reductive elimination. Reductive elimination of the C-N or C-0 fragments should be faster than 13-hydride elimination in order to avoid reduction of the aryl moiety. The side-reaction is shown at the bottom of Figure 13.25. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

Carbon-Oxygen Bond Formation. CAN is an efficient reagent for the conversion of epoxides into /3-nitrato alcohols. 1,2-cA-Diols can be prepared from alkenes by reaction with CAN/I2 followed by hydrolysis with KOH. Of particular interest is the high-yield synthesis of various a-hydroxy ketones and a-amino ketones from oxiranes and aziridines, respectively. The reactions are operated under mild conditions with the use of NBS and a catalytic amount of CAN as the reagents (eq 25). In another case, N-(silylmethyl)amides can be converted to A-(methoxymethyl)amides by CAN in methanol (eq 26). This chemistry has found application in the removal of electroauxiliaries from peptide substrates. Other CAN-mediated C-0 bondforming reactions include the oxidative rearrangement of aryl cyclobutanes and oxetanes, the conversion of allylic and tertiary benzylic alcohols into their corresponding ethers, and the alkoxylation of cephem sulfoxides at the position a to the ester moiety. 

The acyl carbon atom is also sp2-hybridised, much more electrophilic than an aryl carbon atom, and highly stabilised by the structure where the negative charge is on the oxygen atom (Figure 12.18). The acyl oxygen atom may, as in acid catalysed alcoholysis of esters, be protonated, before or after the formation of the new carbon-oxygen bond. 

The use of aryl-A3-iodanes for C-heteroatom bond formation at the a-carbon atoms of ketones and / -dicarbonyl compounds, and related transformations of silyl enol ethers and silyl ketene acetals, has been exhaustively summarized in recent reviews (Scheme 27) [5,8]. Reactions of this type are especially useful for the introduction of oxygen ligands (e. g., L2 = OH, OR, OCOR, 0S02R, OPO(OR)2), and have been extensively utilized for the synthesis of a-sulfonyl-oxy ketones and a-hydroxy dimethyl ketals. 

This reaction allows aryl carbon-heteroatom bond formation via an oxidative coupling of arylboronic acids, stannanes or siloxanes with N-H or O-H containing compounds in air. Substrates include phenols, amines, anilines, amides, imides, ureas, carbamates, and sulfonamides. The reaction is induced by a stoichiometric amount of copper(II) or a catalytic amount of copper catalyst which is reoxidized by atmospheric oxygen. 

For the coupling of binaphthyl compounds, the authors note that 0.55 equivalents of PIFA and a temperature below 0 °C are necessary conditions to obtain the best yields (Table 5). Carbon-carbon bond formation occurs between the most highly oxygenated aryl rings of the naphthyl units. 

The formation of an aryl-O bond by the reaction of a phenol with air and moisture stable potassium alkenyl and aryltrifluoroborates was mediated by a copper species. The reaction procedure involved catalytic amounts of Cu(OAc)2 with DMAP as a ligand in the presence of oxygen and molecular sieves. A variety of aliphatic primary and secondary alcohols as well as phenols were suitable reaction partners, thus displaying a broad functional group tolerance (Equation (237)).1025... 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

Two new methodologies have been developed for the preparation of 2-arylthiazoles 35 from 2-aminothiophenol and aryl aldehydes One uses ionic liquid, l-pentyl-3-methylimidazolium bromide ([pmImJBr), under microwave conditions <04CL274> the other involves catalytic amount of scandium triflate in the presence of oxygen <04H(62)197>. The 2-aminobenzothiazole 37 is prepared by means of copper- and palladium-catalyzed intramolecular C-S bond formation <04CC446>. With respect to the 7-nitro-2-aminobenzothiazole 40, a one step synthesis has been developed (38 to 40) <04TL9373>. 

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