4-nitro-5-styrylisoxazoles

The photodimerization of 3-methyl-4-nitro-5-styrylisoxazoles 137 has been studied in the solid state82. Truxillic acids 139 are prepared by the oxidation of the photodimers 138 (equation 69). 

The data on UV-spectroscopy of nitroisoxazoles are rather scarce. It is known that X for 3,5-dimethylisoxazole is 215-220 ran, whereas that for its 4-nitroderivative lies in a field of 250-270 nm depending on the medium (see Table 3.65) [483,499, 1125, 1159], It is shown [483] that for 5-(p-methoxystyryl)- and 5-cinnamylidene derivatives of 3-methyl-4-nitroisoxazole, the absorption band is moved to the longwave area (290 nm, lg e 4.15). The absorption band maxima of 3-methyl-4-nitro-5--styrylisoxazole photodimers lie in field of 268-272 nm. In works of the Italian authors the electron absorption spectra of some derivatives of nitroisoxazole are described [1160],... 

Diethylphosphonomethyl-3-methylisoxazole was alkylated and olefinated by reaction of its anion with alkyl halides and aldehydes <1999S2027>. Reactions of 3-methyl-4-nitro-5-styrylisoxazole with bis-enolizable ketones have been investigated. Michael adducts were obtained in good yields with substoichiometric amounts of base while spiroisoxazolines were the major products when the base was employed in large excess <2002TL4157>. 

Some other activated olefins have been employed as acceptors in Michael reactions with enolates under PTC conditions, using different chiral ammonium salts as catalysts. For example, a very recent and elegant report has shown that conveniently substituted heterocyclic moieties can also play the role of suitable electron releasing groups for the activation of an olefin toward conjugate addition. In particular 4-nitro-5-styrylisoxazoles were found to undergo clean... 

Scheme 5.32 Enantioselective Michael reaction using 4-nitro-5-styrylisoxazoles as Michael acceptors.

Chiral y-amino acids and y-nitroesters have been prepared, under PTC conditions, from 4-nitro-5-styrylisoxazoles, derivatives efficiently used as cinnamate equivalents in the asymmetric Michael reaction with nitroalkanes[181]. The reaction is catalyzed by Cinchonidine-derived catalyst 122 (2-5 mol%) at low temperatures (-30 to 0°C) affording high selectivities not only with nitromethane but also with secondary and tertiary nitroalkanes as nucleophiles. As seen in Scheme 2.66, the... 

Scheme 2.66 Asymmetric Michael addition of nitroalkanes to 4-nitro-5-styrylisoxazoles...

Racemic Michael addition of 5-nucleophiles, such as PhCH2SH, to 3-methyl-4-nitro-5-styrylisoxazoles (240) can be effectively catalysed by piperidine (10mol%) in MeCN. Nitroisoxazoles (240) also undergo regio- and diastereo-selective trifluo-romethylations at the 5-position by nucleophilic addition using Me3SiCF3. ... 

The NHC-catalysed umpolung of enals into homoenolate equivalents is an efficient tactic to develop cyclization reactions. Substituted cyclopentanones (132) have been prepared in a diastereoselective manner via the reaction of enals and 4-nitro-5-styrylisoxazoles (133) in the presence of imidazolium salt (134) as... 

The II and 13C NMR spectra of 3-methyl4-nitro-5-styrylisoxazole photodimers [498] and other nitroisoxazole derivatives [499, 500] have been examined. 

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