2-alkoxy-1,3,3-tri

Arene-bound alkoxy or amino groups will facilitate oxidation by SET only if their lone electron pairs can interact with the aromatic Jt-system. For this reason 1,3,5-tris(dialkylamino)benzenes will be significantly more air-sensitive than, for instance, l,2,3-tris(dialkylamino)benzenes, because steric crowding in the latter will force the lone pairs into the plane of the arene, where efficient conjugation with the aromatic jt-system is impossible. 

Molybdenum, tris(phenylenedithio)-structure, 1,63 Molybdenum alkoxides physical properties, 2,346 synthesis, 2,339 Molybdenum blue liquid-liquid extraction, 1,548 Molybdenum cofactor, 6,657 Molybdenum complexes acrylonitrile, 2,263 alkoxides, 3,1307 alkoxy carbonyl reactions, 2,355 alkyl, 3,1307 alkyl alkoxy reactions, 2,358 alkyl peroxides oxidation catalyses, 6,342 allyl, 3,1306... 

Niobium, tris(diethyldilhiocarbamato)oxy-stereochemistry, 1,82 structure, 1, 83 Niobium, tris(oxa ato)oxy-stereochcmistry, 1, 82 Niobium, tris(phcnylcncdirhio)-structure, 1, 63 Niobium alanate, 3, 685 Niobium complexes alkyl alkoxy reactions, 2, 358 amides, 2,164 properties, 2, 168 synthesis, 2, 165 applications, 6,1014 carbamicacid, 2, 450 clusters, 3, 672,673,675 hexamethylbenzene ligands, 3, 669 cyanides synthesis, 2, 9 p-dinitrogen, 3, 418 fluoro... 

AuBerst selektive 1,2-Reduktionsmittel sind Bis-[2-methyl-propyl]-aluminiumhydrid1, Tris-[2-methyl-propyl]-aluminium2, Natrium-bis-[2-methyl-propyl]-dihydrido-aluminat3 und besonders 9-Bora-bicyclo[3.3. ljnonan4 (9-BBN, S. 7). Letzteres ergibt zuerst ein Alkoxy-boran, das zweckmaRig mit 2-Amino-athanol gespalten wird. 

In early studies of these reactions, the turnover efficiency was not always high, and stoichiometric amounts of the promoters were often necessary to obtain reasonable chemical yields (Scheme 105) (256). This problem was first solved by using chiral alkoxy Ti(IV) complexes and molecular sieves 4A for reaction between the structurally elaborated a,/3-unsaturated acid derivatives and 1,3-dienes (257). Use of alkylated benzenes as solvents might be helpiul. The A1 complex formed from tri-methylaluminum and a C2 chiral 1,2-bis-sulfonamide has proven to be an extremely efficient catalyst for this type of reaction (258). This cycloaddition is useful for preparing optically active prostaglandin intermediates. Cationic bis(oxazoline)-Fe(III) catalysts that form octahedral chelate complexes with dienophiles promote enantioselective reaction with cyclopentadiene (259). The Mg complexes are equally effective. 

Under conditions of the Hilbert-Johnson reaction, the 2,4-dialkoxypyrimidines (29) can furnish the following by-products uracil,13 1-alkyluracil,3-7 1,3-dialkyluracil,19 4-alkoxy-2(lIZ)-pyri-midinone,7 and l-alkyl-4-alkoxy-2(lH)-pyrimidinone.7,20 Thus, for example, 5-chloro-, 5-bromo-, and 5-iodouracil were isolated32- 33 as by-products in the Hilbert-Johnson reaction (in acetonitrile at 20°) of the corresponding 5-halo-2,4-dimethoxypyrimidines and 3,5-di-O-p-toluyl-2-deoxy-D-ribofuranosyl chloride. The formation of 1,3-dimethyluracil and 1,3,5-trimethyluracil as by-products has been observed quite recently19 when the reaction of 2,3,5-tri-O-benzoyl-D-ribofuranosyl chloride with 2,4-dimethoxypyrimidine and 5-methyl-2,4-dimethoxypyrimidine, respectively, was performed in toluene at 70°. 

Scheme 1 shows the desired Heck reaction of alkoxy-DSB 1 with 2. The formation of 3 is accompanied by two destructive pathways the reductive debromination of 1 to 4 as a side reaction and the protodesilylation to 5 as a subsequent reaction. Particularly the latter limits the reaction conditions in terms of time and temperature. The phosphine is a decisive factor in this system consisting of three reactions a fine-tuning of the reaction conditions is possible via electronic and steric effects of the substituents in the phosphine electron-rich trialkylphosphines 6 and 7 strongly favor the reduction. Fast coupling reactions were observed with tris-o-tolylphosphine 8, the chelating diphosphine dppe 9 being even more efficient in terms of turnover, yield, and suppression of side reactions. Compared with Heck reactions of polycyclic or electron-deficient arenes with 2 [21, 22], the yield of 3 is only moderate. The reactivity of bromo-distyrylbenzenes 1 and 12 -14 in the coupling reaction is controlled by the substituents on the opposite side of the n-system (Fig. 1, Table 2) a compensation for the electron-donating alkoxy groups by a cyanide (13) or exchange of donors with electronically neutral alkyl side chains strongly improves the yields.

A similar reaction is found in the alkaline degradation of picrocrocin [(—)-4-hydroxy-2,6,6-trimethyl-l-cyclohexene-l-carboxaldehyde /3-n-glu-copyranoside] (XXXVIII) to n-glucose and safranal (2,6,6-tri-methyl-1,3-cyclohexadiene-l-carboxaldehyde) (XXXIX) (see Fig. 12). Picrocrocin does not contain a /3-alkoxy carbonyl system, but a proton may be easily removed from C3 of the aglycon by a base (because, as this compound is the vinylog of a d-alkoxy carbonyl compound, these protons behave as if they were adjacent to the carbonyl group). 

It has been shown that it is possible to reverse the diene character of the 1,2,4-triazine ring by introducing alkoxy or dialkylamino groups into the ring.413 Alkoxy-, dialkoxy- and (dialkyl-amino)- ,2,4-triazines are less reactive toward ynamines, however they can still react with these dienophiles. Bis(dialkylamino)-, trialkoxy and tris(dialkylamino)-l,2,4-triazines behave as electron-rich dienes and give cycloaddition reactions with acetylenedicarboxylates, but not with ynamines. For example, A./V./V",TV, TV 1A,"-hexamcthyl-l,2,4-triazinc-3,5,6-triamine and dimethyl acetylenedicarboxylate react to afford pyrimidine 28.413... 

Perhaps structurally the most simple primary amide gelators, 3,4,5-tris-(alkoxy) benzamides 1 and 2 (Fig. 1), have been prepared by amidation of tris(alkoxy)benzoic acids and shown to gel both polar (MeOH, EtOH, DMF) and highly lipophilic organic solvents (n-octane, w-decane, toluene) at minimal gelation concentrations (mgc) lower than 2.5 wt % [5]. The gel aggregates can be embedded into cross-linked polymer matrices using monomer/cross-linker mixtures as organic solvents. 

Syntheses of Fluorouracil prodrugs relied on either chemical modification of 1 or direct fluorination of the corresponding pyrimidine derivatives. In particular, Tegafur (3) was obtained from 1 by reaction with 2,3-dihydrofuran [49-54], 2-chloro- [55, 56], 2-alkoxy- [57], 2-acetoxytetrahydrofuran [58, 59, 300], and 4-tri-methylsilyloxybutyraldehyde dimethyl acetal (48) (Scheme 9) [60]. Alternatively, 3 was prepared via fluorination of compound 49 [61] or ester 50 [62],... 

Whereas ethers of monohydric alcohols or phenols are denoted by alkoxy-, aryloxy-, efe., prefixes or as the -yl -yl ether (with the radical prefixes in alphabetical order), those from polyhydric alcohols and phenols are handled differently. Either the monohydric component is written first, with unchanged -ol ending, as in glycerol 1-ethyl ether, glucose 2,3,6-trimethyl ether or the ether groups are added by means of 0- prefixes, as in 2,3,6-tri-O-methylglucose, 1-0-ethylpyrogallol. The same alternatives exist for esters of polyhydric alcohols. 

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