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Spiro adducts

The 5-methylene-2(5//)-furanone 216 was found to be a good dienophile in Diels-Alder reactions with acyclic dienes (R = H, 2-Me, 2,3-di-Me, 1-Me, 1,3-di-Me). The reaction took place specifically at the cxo-cyclic double bond to give the corresponding spiro adducts 217 in good yields (Scheme 59) (90JOC3060). [Pg.144]

Reactions of arylsulfonylallenes with 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide (227) proceed in a manner similar to that of the above-mentioned sulfides. Probably, both 4- and 5-alkylidene-4,5-dihydroisoxazole cycloadducts are initially formed which then undergo different transformations. 4-Alkylidene isomers give spiro adducts such as 60 with an additional molecule of nitrile oxide, while 5-isomers convert to isoxazoles 61, products of their prototropic rearrangement. [Pg.29]

Dipolarophiles D9. Various a-methylenelactams D9" (n = 0,1,2) with four-to six-membered rings (Table 2.25), in reactions with nitrones (637), (Table 2.26) afforded good yields of spiro adducts (638) and (639) via regiospecific... [Pg.354]

N-Tosyl- and N-benzoyl-4-vinylidene-2-oxazolidinones underwent [4 + 2]-cycloaddi-tions with MVK at the enamide double bond to furnish the spiro adducts [154]. [Pg.789]

Diazo-2-oxindole (21c) reacted with benzyne and dimethyl acetylene-dicarboxylate in dichloromethane at 41°C to give polycyclic ring systems of type 265 (73TL1417) (Scheme 78). The intermediate spiro adducts 264 could not be detected, but it is reasonable to suppose that the final products were obtained by [1,5]sigmatropic rearrangement of the carboxamido moiety. [Pg.147]

Reactions with Other Nucleophiles in Aqueous Solution Spiro Adducts. . 433... [Pg.306]

Evidence for the formation of Meisenheimer-type adducts from a purine system has been obtained by Liotta in two cases.43 The addition of t-BuO to 6-(2-hydroxyethoxy)-9-methoxymethyIpurine in t-BuOH, as monitored by H-NMR spectroscopy, causes an upfield shift of both pyrimidine and imidazole ring protons and the conversion of two absorptions of the methylene protons of the CH2CH2OH group to a broad absorption of the dioxolane ring, in agreement with the formation of the spiro adduct 19. Similarly, adduct 20 was formed from 6-methoxy-9-methoxymethylpurine by slow reaction with MeCT in 7-BuOH. [Pg.323]

Two substrates of special interest are 2-(2-hydroxyethoxy)-3-nitro-thiophene and its 3-(2-hydroxyethoxy)-2-nitro isomer. Both compounds form Meisenheimer-type spiro adducts, 135 and 136, by ring closure at the 2-and 3-positions, respectively.177 Intramolecular cyclization brings in an extra driving force for the formation of the adduct, which is also observed in the trinitrobenzene series.31 This would account for the structure of adduct 136, which exceptionally bears the sp3-hybridized carbon on a ft position. No other examples of such a structure from 5-membered heteroaromatic substrates is known even for transient species, except for benzoannelated derivatives (see Section III,A,3). [Pg.393]

By addition of one equivalent of base to solutions of 7-(2-hydroxyethoxy)-4-nitrobenzofurazan and 7-(2-hydroxyethoxy)-4-nitrobenzofuroxan in either water or a dipolar aprotic solvent, the spiro adducts 169 and 170 are completely formed212 and can be characterized by their UV-visible and H-NMR spectra. They display substantial upfield chemical shifts relative to the ring signals for the starting substrate and a complex multiplet centered at 8 4.16 for the nonequivalent dioxolane methylene protons. Isolation of the adducts as the potassium salts from acetonitrile solution was accomplished by removal of the solvent. [Pg.422]

The formation of pyrazolo[l,5-a]pyridines from diazocyclopentadienes was discussed in Section II,1,4,a The cyclopentanone 261 was converted to the corresponding reduced product 262 upon treatment with dipolarophiles, possibly involving [l,5]-sigmatropic rearrangement of the intermediate spiro adduct.212... [Pg.393]

NMR evidence has been provided for the formation of Meisenheimer adducts in DMSO solution from several mononitrothiophenes (70JHC1441, 74JHC97, 75JHC327). Interesting examples of the formation of spiro adducts have also been recorded (Scheme 137) (75JHC1083) one of these appears to be the first Meisenheimer complex observed at position 3 of thiophene. [Pg.816]

The reaction of 7-chloro-4,6-dinitrobenzofurazan with 2-(4,-bromophenyl)indolizine has been shown to result in carbon-carbon bond formation by substitution of the 7-chloro substituent.58 However, in the reaction of 7-chloro-4,6-dinitrobenzofuroxan the initial substitution is followed by intramolecular oxygen transfer from the N-oxide function and by rearrangement to give the zwitterionic spiro-adduct (15). An... [Pg.184]

Excellent yields are also obtained in spiro-adducts formed by the condensation of azomethine ylid thus generated, with 3-arylidene-flavanone derivatives at room temperature in the presence of trifluomethylacetic acid in toluene. These molecules are both flavonoids and spiro compounds, two classes of naturally occurring substances which exhibit biological activities 419... [Pg.318]

A spiro adduct is the result of the reaction of diazofluorene and perflu-oro-2-butyne (72AG(E)224, 72TL3479 74CB2027). With diazomethane and ethyl diazoacetate the above-mentioned trifluoromethyl-substituted alkynylamino and alkynyl hydroxy acid esters give a single [3 -t- 2] cycloadduct, namely the 2-(3-pyrazolyl)-3,3,3-trifluoroalanine and the 2-(3-pyrazolyl)-3,3,3-trifluorolactic acid derivatives, respectively (92LA947) (Scheme 71). [Pg.37]

Machacek, V., Hassanien, M. M. H., Sterba, V. Kinetics and mechanism of spiro adduct formation from and Smiies rearrangement of N-methyi-N-(2,4,6-trinitrophenyi)aminoacetaniiide. Base-cataiyzed transformation of N-(2,4,6-trinitrophenyiamino)acetaniiide into 2-nitroso-4,6-dinitroaniiine. Collect. Czech. Chem. Commun. 1987,52,2225-2240. [Pg.679]

Cycloaddition of benzyne to 3-diazooxindole (99) led, via rearrangement of the spiro adduct 100, to the condensed indazole derivative 101 (91%), the structure of which was confirmed by an independent synthesis.76... [Pg.204]

Similar palladium-catalyzed intramolecular dicarborations of dienes using aryl or vinyl halides and tributyl(vinyl)tin as reagents are known39,69. Thus, dienamide 2, containing the chiral pinene skeleton, gives the heterocyclic spiro adduct 3 with complete control of stereochemistry69. [Pg.445]

Photoaddition of p-benzoquinone to unsymmetrical keten dimers gives the spiro-adduct (70) together with (71) and (72), which are thought to arise by... [Pg.64]

Such reactions have been recorded for unsubstituted [85,89,91,92], phenyl- [90,93,94] and halogeno-diazocyclopentadienes [64,65]. Allene also provides a spiro-adduct [95]. Sometimes insertion products are also formed [85,93,96] it has been suggested that the main controlling factors appear to be steric. Insertion reactions ensue when diazocyclopentadienes are irradiated in cycloalkanes [53,64], methanol [53] or carbon tetrachloride [64]. [Pg.24]

A set of exocyclic methylene benzo-l,2-thiazepine dioxides underwent 1,3-dipolar cycloaddition reactions with benzonitrile oxide to give isoxazo-line Spiro adducts 139 in a regioselective, and for specific dipolarophiles, diastereoselective manner (14AJC381). Guided by X-ray crystallographic analysis, a pair of benzo-l,2-thiazepine dioxides 140 was designed, prepared, and found to be picomolar inhibitors of HIV-1 protease (14T2894). [Pg.552]


See other pages where Spiro adducts is mentioned: [Pg.79]    [Pg.34]    [Pg.324]    [Pg.49]    [Pg.26]    [Pg.186]    [Pg.79]    [Pg.320]    [Pg.340]    [Pg.433]    [Pg.434]    [Pg.439]    [Pg.440]    [Pg.79]    [Pg.185]    [Pg.204]    [Pg.3323]    [Pg.256]    [Pg.278]    [Pg.79]    [Pg.278]    [Pg.358]    [Pg.3322]    [Pg.1159]    [Pg.245]    [Pg.65]    [Pg.247]   
See also in sourсe #XX -- [ Pg.495 ]




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