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1.3- Dipolar cycloaddition intramolecular silyl nitronate

TABLE 2.39. INTRAMOLECULAR DIPOLAR CYCLOADDITION OF SILYL NITRONATES... [Pg.123]

The 3 + 2-cycloaddition of nitrile oxides to 2-crotyl-l,3-dithiane 1-oxides produces exclusively 5-acyldihydroisoxazoles.92 Lewis acid addition to 1,3-dipole cycloaddition reactions of mesityl nitrile oxide with a, /i-unsaturated 2-acyl-1,3-dithiane 1-oxides can reverse the sense of induced stereoselectivity.93 The 1,3-dipolar cycloaddition of 4-t-butylbenzonitrile oxide with 6A-acrylainido-6A-deoxy-/i-cyclodextrin (68) in aqueous solution favours the formation of the 4-substituted isoxazoline (69) rather than the 5-substituted regioisomer (Scheme 24).94 Tandem intramolecular cycloadditions of silyl nitronate, synthons of nitrile oxides, yield functionalized hydrofurans.95... [Pg.441]

One-pot tandem sequences involving 1,4-addition and ISOC as the key steps have been developed for the construction of N and 0 heterocycles as well as of carbocycles [44]. In this sequence, the nitronate arising from 1,4-addition to an a, -unsaturated nitro alkene is trapped kinetically using trimethyl silyl chloride (TMSCl). The resulting silyl nitronate underwent a facile intramolecular 1,3-dipolar cycloaddition with the unsaturated tether (e.g.. Schemes 20-22). [Pg.23]

The use of silylketals derived from allylic alcohols and 1-substituted nitroethanols for the stereocontrolled synthesis of 3,4,5-trisubstituted 2-isoxazolines via intramolecular 1,3-dipolar cycloaddition has been demonstrated. Here again, the use of silyl nitronates (ISOC) increases the level of selectivity compared to INOC (Eq. 8.92).145... [Pg.274]

On the other hand, compound 245 was submitted to m-CPBA oxidation and the resulting N-oxide intermediate underwent a Cope reaction in acidic conditions to give N-hydroxypyrrolidine 246 in 77% yield (Scheme 41). The final steps of the synthesis were devoted to the construction of the intramolecular nitrone connection. For this purpose, appHcation of the Mukaiyama conditions generated in a regioselective fashion the nitrone intermediate, which collapsed via an intramolecular 1,3-dipolar cycloaddition to the required strained adduct. Final silyl deprotection furnished virosaine A (38) in 81% yield. [Pg.96]


See other pages where 1.3- Dipolar cycloaddition intramolecular silyl nitronate is mentioned: [Pg.103]    [Pg.346]    [Pg.1023]    [Pg.83]    [Pg.264]    [Pg.244]   


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