Alkoxy-substituted

The method has not been studied extensively and is restricted to the preparation of alkyl-, aryl-, or alkoxy-substituted thiazoles mostly in 2-, 5-, or 2,5-positions. Yields ranged from 45 to 80%. Sometimes this method gives good results when the usual Hantzsch s synthesis fails. There has been very little speculation about the mechanism of this reaction. 

The standard manufacturing method for tetraalkyl titanates, such as TYZOR TPT, or tetra- -butyi titanate, TYZOR TBT [5593-70 ] involves the addition of TiCl to an alcohol. In a series of reversible displacement reactions, the alkoxy substitution products and hydrochloric acid form as follows ... 

Heteroaromatic ring stmctures can also be incorporated into poly(arylene vinylene) stmctures using the same precursor polymer method shown for PPV. Poly(thienylene vinylene) (13) (113—118) and poly(furylene vinylene) (14) (119,120) have been prepared in this manner. In addition, alkoxy-substituted poly(thienylene vinylenes) (15) (119,121) have been synthesized. Various copolymers containing phenjiene, thienylene, and furylene moieties have also been studied (120,122,123). 

Nitronates derived from primary nitroalkanes can be regarded as a synthetic equivalent of nitrile oxides since the elimination of an alcohol molecule from nitronates adds one higher oxidation level leading to nitrile oxides. This direct / -elimination of nitronates is known to be facilitated in the presence of a Lewis acid or a base catalyst [66, 72, 73]. On the other hand, cycloaddition reactions of nitronates to alkene dipolarophiles produce N-alkoxy-substituted isoxazolidines as cycloadducts. Under acid-catalyzed conditions, these isoxazolidines can be transformed into 2-isoxazolines through a ready / -elimination, and 2-isoxazolines correspond to the cycloadducts of nitrile oxide cycloadditions to alkenes [74]. 

Conjugate addition reactions of acyclic Midiael acceptors possessing betetoatom-SLibstituted stereogenic centers in tlieir )>-positions may provide usefiil levels of diastereoselectivity. A typical example is given witli tlie y-alkoxy-substituted enoate 49 in Sdieme 6.8 [17]. High levels of diastereoselectivity in favor of tlie anii addition product SO were found in tlie course of dlmediylcuprate addition. 

Substituted soluble PPV derivatives may also be synthesized by step-growth polymerization methods. Arylene-fc/.v-phosphylidenes may be condensed with ler-ephthaldehydes in a Wittig fashion to yield alternating PPV copolymers [52]. An alkoxy-substituted PPV derivative 28 (Scheme 1-8) prepared in this fashion emits in the orange (2nmx=585 nm) region of the spectrum [52]. 

The sulfonium precursor route may also be applied to alkoxy-substituted PPVs, but a dehydrohalogenation-condensation polymerization route, pioneered by Gilch, is favored 37]. The polymerization again proceeds via a quinomethide intermediate, but die syndicsis of the conjugated polymer requires only two steps and proceeds often in improved yields. The synthesis of the much-studied poly 2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene], MEH-PPV 15 is outlined in Scheme 1-5 33, 35]. The solubility of MEH-PPV is believed to be enhanced by the branched nature of its side-chain. 

The optical properties can be tuned by variations of the chromophores (e.g. type of side-chains or length of chromophorc). The alkyl- and alkoxy-substituted polymers emit in the bluc-gnecn range of the visible spectrum with high photolu-inincsccncc quantum yields (0.4-0.8 in solution), while yellow or red emission is obtained by a further modification of the chemical structure of the chromophores. For example, cyano substitution on the vinylene moiety yields an orange emitter. 

The data reported in Table 3 for the 2-butenylborations of 2-(dibenzylamino)propanal shed additional light on this transition state model. The ( )-2-butenylboration of 2-(dibenzyl-amino)propanal evidently proceeds preferentially (90%) by way of transition state 9, suggesting that the bulky dibenzylamino substituent destabilizes transition state 8 (X = NBn2 > CH3). On the other hand, the (Z)-2-butenylboration of 2-(dibenzylamino)propanal is relatively non-selective, compared to the excellent selectivity realized in the (Z)-allylborations of a-chloro- or x-alkoxy-substituted chiral aldehydes. This result suggests that an increase in the steric requirement of X destabilizes transition state 11 such that significantly greater amounts of product are obtained from transition state 10. 

The tartrate ester modified allylboronates, the diisopropyl 2-allyl-l,3,2-dioxaborolane-4,5-di-carboxylates, are attractive reagents for organic synthesis owing to their ease of preparation and stability to storage71. In the best cases these reagents are about as enantioselective as the allyl(diisopinocampheyl)boranes (82-88% ee with unhindered aliphatic aldehydes), but with hindered aliphatic, aromatic, a,/l-unsaturated and many a- and /5-alkoxy-substituted aldehydes the enantioselectivity falls to 55-75% ee71a-b... 

Alkoxy-substituted allylaluminum reagents diethyl[(Z)-3-methoxy-2-propenyl]- and -[(Z)-3-(l-methoxy-l-methylethyl)-2-propenyl]aluminum have been prepared by treatment of the corresponding alkoxyallyllithiums with diethylaluminum chloride in tetrahydrofuran at — 78 =C4. These reagents provide the syn-diastereomer with 9-11 1 selectivity in reactions with aldehydes at — 78 °C. The reaction of diethyir(Z)-3-methoxy-2-propenyl]a]uminum and acetophenone provided the iy -diastereomer with 4 1 selectivity. 

The lithium 2-butenyl(triethyl)aluminate complex, prepared in situ from 2-butenyllithium and triethylaluminum, displayed poor diastereoselectivity in a reaction with benzaldehyde (anti/syn 56 44)7. (Z)-3-Alkoxy-substituted aluminate complexes such as A-C, however, give good diastereoselectivity in aldehyde addition reactions8. The reactions of A with aldehydes at —100 °C give the jyw-diol monoether with >95% diastereoselectivity and >80-95% regiose-... 

The heteroatom-substituted ate complexes 3 (Y = S-z-Pr, SeC6H5 or TMS) have also been examined, but their reactions with aldehydes are not as regio- or stereoselective as those of the alkoxy-substituted reagents 8b. 

The a-alkoxy-substituted iron-acyl complex 8 is prepared by oxidation of the enolate prepared from iron-acetyl complex 6 and subsequent etherification12. 

The lithium enolate of a-alkoxy substituted complex 9 also exhibited little selectivity upon reaction with aldehydes all four possible diastereomers were produced when it was treated with acetaldehyde49. 

Treatment of a-alkoxy-substituted iron acyl complexes 20 with bromine in the presence of an alcohol produces free acetals 22 with loss of stereochemistry at the center derived from the a-carbon of the starting complexl2,49. Electron donation from the alkoxy group allows formation of the oxonium intermediate 21, which is captured by the alcohol to generate the product acetal. 

A further extension of the MIMIRC reaction is seen in the synthesis of enantiomerically pure cyclohexanones. A successful diastereoselective MIMIRC reaction with 2-(rer/-butyldimethylsi-lyloxy)-4-phenyl-l,3-butadiene and an optically pure (Z)-y-alkoxy-substituted enone was performed using catalytic amounts (5 mol%) of triphenylmethyl perchlorate at — 78 ,C 360,408 (for a further example see Section 1.5.2.4.4.1.). 

The model process Eq. (15) has been studied by means of the MINDO/3 method to clarify the energetic conditions during the formation of cyclic reactive intermediates in cationic propagation of alkoxy-substituted monomers. The enthalpies of formation in the gas phase AH°g of both the alternative structures e and /were supplemented by the solvation energies Eso]v for transition into solvent CH2C12 with the assistance of the continuum model of Huron and Claverie which leads to heats of formation in solution AH° s. Table 13 contains the calculated results. 

Abstract In this paper the synthesis, properties and applications of poly(organophos-phazenes) have been highlighted. Five different classes of macromolecules have been described, i.e. phosphazene fluoroelastomers, aryloxy-substituted polymeric flame-retardants, alkoxy-substituted phosphazene electric conductors, biomaterials and photo-inert and/or photo-active phosphazene derivatives. Perspectives of future developments in this field are briefly discussed. 

Horhold et al. and Lenz et al. [94,95]. The polycondensation provides the cyano-PPVs as insoluble, intractable powders. Holmes et al. [96], and later on Rikken et al. [97], described a new family of soluble, well-characterized 2,5-dialkyl- and 2,5-dialkoxy-substituted poly(pflrfl-phenylene-cyanovinylene)s (74b) synthesized by Knoevenagel condensation-polymerization of the corresponding alkyl-or alkoxy-substituted aromatic monomers. Careful control of the reaction conditions (tetra-n-butyl ammonium hydroxide as base) is required to avoid Michael-type addition. 

Meier et al. have also contributed to the field of cyclic PAV oligomers with the synthesis of cyclic dl -trans (all- ) trimers (e.g. 113) containing alkoxy-substituted 1,7-naphthylene and 1,9-phenanthrylene building blocks, via a Siegrist-type trimerizing olefination [134,135]. Suitable substitution at the periphery of the cyclic trimers allows for the formation of stable, thermotropic discotic mesophases [134]. 

B. Structure.—The crystal structure of l,l-bis(dimethylamino)-2,4,6-triphenylphosphorin shows that this compound is very similar in structure to the 1-alkyl- and 1-alkoxy-substituted phosphorins. ... 

Use of oxygenated stannanes with a-substituted aldehydes leads to matched and mismatched combinations.181 For example, with the y-MOM derivative and a-benzyloxypropanal, the matched pair gives a single stereoisomer of the major product, whereas the mismatched pair gives a 67 33 syntanti mixture. The configuration at the alkoxy-substituted center is completely controlled by the chirality of the stannane. 

Scheme 10.12 gives some examples of enantioselective cyclopropanations. Entry 1 uses the W.s-/-butyloxazoline (BOX) catalyst. The catalytic cyclopropanation in Entry 2 achieves both stereo- and enantioselectivity. The electronic effect of the catalysts (see p. 926) directs the alkoxy-substituted ring trans to the ester substituent (87 13 ratio), and very high enantioselectivity was observed. Entry 3 also used the /-butyl -BOX catalyst. The product was used in an enantioselective synthesis of the alkaloid quebrachamine. Entry 4 is an example of enantioselective methylene transfer using the tartrate-derived dioxaborolane catalyst (see p. 920). Entry 5 used the Rh2[5(X)-MePY]4... 

Wolleb, H. (Ciba-Geigy). Process for the Preparation of Brominated, Alkoxy-Substituted Metal Phthalocyanines. U.S. Patent 5,594,128, January 14, 1997. 

Stepanov et a/.143,144 report the ring opening of the monoxide (116) to several 2-oxaadamantane derivatives, where 116 is readily obtained by perbenzoic acid oxidation of 35. Treatment of 116 under various conditions yields different products. Thus, with aqueous acid it yields l-hydroxy-3-hydroxymethyl-2-oxaadamantane (117), with alcohols (R = CH3, C2H5) in acidic or basic media 1-alkoxy-substituted (118), and with hydrochloric acid l-chloro-3-hydroxymethyl-2-oxaadamantane(119). l-Methyl-2-oxaadaman-tane (120) is prepared by LAH reduction of the carbonyl group in 35 to alcohol 121 and subsequent cyclization with acid.140,142... 

A) Phenols of this group react with peroxyl radicals, hydroperoxide, and dioxygen, while respective phenoxyl radicals can react with RH and ROOH. Reactions of these phenols with R02 most commonly give rise to quinones the breakdown of phenoxyls does not produce active radicals. This group includes all phenols, except 2,6-di-/er/-alky I phenols and alkoxy-substituted phenols. Phenols of this group can inhibit oxidation by mechanisms I-VII. 

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