Phenols, reaction with acetylenic esters

The reaction of few phenols with acetylenic esters is reported in the literature. " George and co-workers, on the basis of detailed nuclear magnetic resonance (NMR) studies of the product mixtures formed in the reaction of several phenols with DMAD, have concluded that, as the size of the attacking nucleophile increases, there is a greater tendency for the formation of maleates, which are sterically more favored as compared to the fumarates. 

Nair 482 reacted benzoxazole with a molar quantity of DM AD at room temperature for 10 days, then he heated the product for 6 hours at 100°, and obtained 3-methoxycarbonylmethylene-2-oxo-3,4-dihydro-2H-1,4-benzoxazine (18), identical with that obtained from o-amino-phenol and the acetylenic ester his benzoxazole may have hydrolyzed before or during reaction. 

Besides simple enones and enals, less reactive Michael acceptors like /3,/3-disubstituted enones, as well as a,/3-unsaturated esters, thioesters, and nitriles, can also be transformed into the 1,4-addition products by this procedure.44,44a,46,46a The conjugate addition of a-aminoalkylcuprates to allenic or acetylenic Michael acceptors has been utilized extensively in the synthesis of heterocyclic products.46-49 For instance, addition of the cuprate, formed from cyclic carbamate 53 by deprotonation and transmetallation, to alkyl-substituted allenic esters proceeded with high stereoselectivity to afford the adducts 54 with good yield (Scheme 12).46,46a 47 Treatment with phenol and chlorotrimethylsilane effected a smooth Boc deprotection and lactam formation. In contrast, the corresponding reaction with acetylenic esters46,46a or ketones48 invariably produced an E Z-mixture of addition products 56. This poor stereoselectivity could be circumvented by the use of (E)- or (Z)-3-iodo-2-enoates instead of acetylenic esters,49 but turned out to be irrelevant for the subsequent deprotection/cyclization to the pyrroles 57 since this step took place with concomitant E/Z-isomerization. 

REPPE PROCESS. Any of several processes involving reaction of acetylene (1) with formaldehyde to produce 2-butync-l,4-diol which can be converted to butadiene (2) with formaldehyde under different conditions to produce propargyl alcohol and, form this, allyl alcohol (3) with hydrogen cyanide to yield acrylonitrile (4) with alcohols to give vinyl ethers (5) with amines or phenols to give vinyl derivatives (6) with carbon monoxide and alcohols to give esters of acrylic acid (7) by polymerization to produce cyclooctatetraene and (8) with phenols to make resins. The use of catalysis, pressures up to 30 atm, and special techniques to avoid or contain explosions are important factors in these processes. 

Examples of the protection of acetylenes, carboxylic acids, alcohols, phenols, aldehydes, amides, amines, esters, ketones, and alkenes are also presented. Sections (designated with an A 15A, 30A, etc.) are labeled protecting group reactions and are located at the end of pertinent chapters. 

The Diels-Alder reaction of furans has been studied in detail [4a]. With acetylenic dienophiles, e.g. acetylenedicarboxylic ester, adducts are formed (e.g. 3) which are isomerized by acids to phenols. The selective hydrogenation of 3 to 4 followed by a [4+2] cycloreversion yields the 3,4-disubstituted furan 5 ... 

The reaction of bicyclic phosphoramidites with alcohols offers a simple route to hydridophosphoranes. In particular the oxidative addition of a variety of alcohols (ROH) or phenol (PhOH) with bicyclic phosphoramidites of type (107) give a wide range of bicyclic phosphoranes of type (108) with the P-H bond in an equatorial position. A number of addition reactions with activated double (e.g. fumaric ester) and triple (e.g. acetylene dicarboxylic ester) bonds arc also dcscribcd. The reaction of hydridophosphoranes (109) with alcohols (1 lOa-0 takes a further step in the presence of diphenyl disulphide to generate the alkoxylated products (llla-f). ... 

The gas-phase equilibrium between 2-hydroxypyridine and 2-pyridone favours the hydroxy-form, but in the equilibrium between 2-hydroxypyridine iV-oxide and N-hydroxy-2-pyridone, the major tautomer is the hydroxy-pyridone. Bicyclic adducts between 2-pyridones and dimethyl acetylene-dicarboxylate, unobtainable at atmospheric pressure, have been obtained at 10—15 kbar. A novel route to iV-hydroxy-2-pyridone involves the trimethyl-silylation of 2-pyridone followed by oxidation of the resulting 2-(trimethyl-silyloxy)pyridine with the DMF complex of molybdenum pentoxide. p-Nitro-phenols (45) and nitro-acetamides (46) are formed from the reaction of 3,5-dinitro-2-pyridones (43) with the sodium salts of /3-keto-esters (44) (Scheme 20). ... 

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