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Bromo substitution

Methylmagnesium chloride has been added to various d-(4-substituted-phenyl) <5-oxo esters 15 (X = H, Cl 13, F, Cl, Br, OC11,) which provides the diastereomeric -lactones 1642. The electronic properties of the phenyl 4-substituent have no significant influence on the diastereoselectivity. Except for the 4-methoxyphenyl compound, which is unreactive even at 60 °C, a ratio of ca. 40 60 in favor of the anti-Cram product is observed at 60 "C in tetrahydrofuran as reaction solvent. Lowering the reaction temperature to 0 °C slightly increases the anti-Cram selectivity in the case of the 4-fluoro-, 4-chloro-, and 4-bromo-substituted compounds. On the other hand, a complete loss of reactivity is observed with the <5-phenyl- and <5-(4-methylphenyl)-substituted h-oxo esters. [Pg.44]

A similar trend was observed in the reaction of tri- and tetrasubstituted etiolates derived from 2-unsubstituted or 2-bromo substituted 3,4-dihydro-6-methoxy-1(2//)-naphthalenone16. The trisubstituted cnolate underwent addition to (—)-(2 )-2-(4-methylphenylsulfinyl)-2-cyclopen-tenone via attack on the nonchelated conformation to give an adduct of d.r. [(2S)/(2/ )] 77 23. The tetrasubstituted enolate underwent addition to the corresponding ( + )-(5)-enone via attack on the chelated conformation to give an adduct with the same absolute configuration at C-2 but with d.r. [(2R) (2S)] 95.5-97 4.5-3. [Pg.1047]

The thiophene-2-sulfonyl radicals without substituents at position 3 exhibit rapid rotation about the C—S bond in the ESR time scale, while the 3-bromo-substituted ones demonstrate a marked conformational preference which has been interpreted in terms of a re-type conjugated structure similar to 3 (cf. entries 10 and 11 in Table 2)10. Calculations... [Pg.1091]

Berthelot et al. have already reported that the reaction of aromatic amines with tetrabutylammonium tribromide (TBA Br3) in chloroform gave p-selective bromo-substituted aromatic amines (ref. 10). We also carried out the bromination of... [Pg.33]

The reaction of acetanilides with tetraalkylanunonium polyhalides, such as TBA Br3, BTMA Bf3, or BTMA Br2Cl in dichloromethane-methanol at room temperature gave bromo-substituted acetanilides in good yields, respectively. These bromination of acetanilides have usually given predominantly the corresponding p-bromo derivatives (Fig. 12) (ref. 17). Furthermore, the reaction of acetanilides with BTMA Br3 in acetic acid in the presence of ZnCl2 gave polybromo-substituted acetanilides which was not obtained from the reactions in dichloromethane-methanol (ref. 18). [Pg.36]

Usually, a-bromo-substituted arenes have been prepared through the reaction of arenes with bromine under ultraviolet irradiation. In the presence of benzoyl peroxide, N-bromosuccinimide can also be used for this purpose. [Pg.37]

We found that the reaction of arenes with a calculated amount of BTMA Br3 in refluxing benzene in the presence of AIBN gave a-bromo-substituted arenes in fairly good yields. In this method, it was found that AIBN was a more effective free radical initiator than benzoyl peroxide (Fig. 15) (ref. 22). [Pg.37]

Lithiation of bromo-substituted aromatic and heteroaromatic derivatives with n-BuLi and subsequent treatment with the chiral chlorophospholane 2 at lower temperature produces the corresponding 2,5-dimethylphospholanes (3-6) in good yields (Scheme 24.1). A two-step approach was used to prepare the diphospholane 3 without isolating the intermediate l-bromo-2-(2,5-(R)-dimethylphospholanyl-l)-acenaphthylene. [Pg.212]

Peroxide ring closures were effected by stirring the 2,3-dibromocycloalkyl hydroperoxides with silver trifluoroacetate, and the bromo-substituted bicyclic peroxides were isolated by silica chromatography at —25 °C. Yields (based on 2-cycloalkenyl hydroperoxide) of 56 and 38% were achieved respectively for the [3.2.1]- and [4.2.11-compounds, but only 16% of the [2.2.1]- and 13% of the [5.2.1]-peroxide was obtained. The main reason for the low yield of the [2.2.1]-peroxide was that substitution by trifluoroacetate, which competes with the desired dioxabicyclization, is particularly prevalent with the 5-membered ring. [Pg.138]

Jakle and Wagner have communicated the synthesis of bromo-substituted, boranediyl-bridged poly(ferrocenylene)s (40) (Fig. 28) by the reaction of Fc(BBr2)2 with three equivalents of HSiEt3. The polymer 40 was transformed into the corresponding mesityl-substituted polymer (40Mes) by treating its slurry in toluene with... [Pg.37]

Figure 28 Synthesis of bromo-substituted, boranediyl-bridged poly(ferrocenylene)s (40) from Fc(BBr2)2. (Adapted from ref. 62.)... Figure 28 Synthesis of bromo-substituted, boranediyl-bridged poly(ferrocenylene)s (40) from Fc(BBr2)2. (Adapted from ref. 62.)...
The bromo-substituted azacyanine 79 undergoes addition of hydroxide ion and then the resultant adduct 80 undergoes ring-opening reaction to form compound 81 in good yield (Scheme 3) <2001JOC1310>. [Pg.1016]

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. [Pg.210]

Haloarenes have been found to undergo nucleopilic substitution when irradiated with the triphenyl stannyl anion46, reacting via a radical S l mechanism. In many cases the reaction will only occur under photochemical conditions. The reaction is found to proceed with chloro- and bromo-substituted arenes, but not iodo-compounds. The anion is produced either by treatment of triphenyltin chloride or hexaphenylditin with sodium metal in liquid ammonia, and will react with a wide variety of arenes (reaction 30). [Pg.736]

Recently, it has been demonstrated (495) that the [3+ 2]-cycloaddition reactions of 3-bromo-substituted six-membered cyclic nitronates (400), which are constructed from olefins (401) and l-bromo-l-nitro-2,4/-methoxyphenylethylene, with olefins (402) produce 3-vinylisoxazolines (403) or five-membered cyclic nitronates (404) in good yields (Scheme 3.221). [Pg.652]

In processes (400 + 402)—>(403) and (400 + 402)—>(404), the possibility of introducing of auxiliaries at the C-6 atom is advantageous for the development of new strategies for asymmetric synthesis with participation of six-membered 3-bromo-substituted six-membered cyclic nitronates. [Pg.652]

CHEC-II(8)421>. Reaction of 94 with water can proceed by two different routes depending on the substitution pattern in the case of the bromo-substituted derivative the unsaturated ketone 97 was formed in high yield, whereas the derivative being unsubstituted at the pyrimidine moiety gave the methyl ester 98, also in very good yield. [Pg.685]

Transformations of various 2-bromo-substituted derivatives of [l,3,4]thiadiazolo[3,2-tf]pyrimidines are shown in Scheme 27. Thus, reaction of 218 with dimethylamine gave 219 in medium yield <2005JHC1105>, treatment of 220 with mercaptans afforded 221 in good yield <1999IZV1154>, whereas reaction of 222 with hetarylamines and hetarylmercaptanes yielded 223 <1993IZV1954, 1994KGS560>. [Pg.697]

Similar conditions as for the formation of PCB s might also lead to the formation of small trace amounts of dioxins. A German Hazardous Substances Ordinance (Chemikalien-Verbotsverordnung) prohibits to place products on the market for which very low limits of dioxin traces are exceeded. Regulated dioxins are those which at least are tetrachloro (or bromo) substituted in 2,3,7,8-position [14],... [Pg.593]


See other pages where Bromo substitution is mentioned: [Pg.21]    [Pg.134]    [Pg.18]    [Pg.128]    [Pg.110]    [Pg.301]    [Pg.70]    [Pg.30]    [Pg.31]    [Pg.32]    [Pg.34]    [Pg.34]    [Pg.37]    [Pg.110]    [Pg.255]    [Pg.96]    [Pg.212]    [Pg.1130]    [Pg.700]    [Pg.201]    [Pg.436]    [Pg.935]    [Pg.56]    [Pg.243]    [Pg.678]    [Pg.137]    [Pg.831]    [Pg.844]    [Pg.28]    [Pg.290]    [Pg.433]   
See also in sourсe #XX -- [ Pg.243 ]




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