Mesityl nitrile oxide, 1,3-dipolar cycloaddition

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... 

C (10 mmHg). In CeD, the PNMR shift was <5 +159, entirely consistent with the presence of a C=P double bond, and this was confirmed by the C NMR spectrum, which showed phosphorus to be directly coupled to an sp carbon (<5 194.7, Jfc 68.7 Hz) and to an sp carbon 37.1, /pc 51.4 Hz). The 27f-phospholes where the 2-phenyl was replaced by 2,4,6-trimethylphenyl, 2,4,6-trimethoxyphenyl, and methyl were also made in good yield by this method. These 2 -phospholes are thermally stable but very sensitive to water and were hydrated on attempted chromatography on Kieselgel to form the phospholanone (204). Other reactions observed (Scheme 46) included a Diels-Alder cycloaddition with methyl propiolate (giving (205)), and a 1,3-dipolar cycloaddition with mesityl nitrile oxide that formed (206). 

Facial selectivity in 1,3-dipolar cycloadditions to cis-3,4-dimethylcyclobutene (73) (Scheme 1.21) was studied. Only phenylglyoxylo- and pyruvonitrile oxides lacked facial selectivities (anti syn = 1 1). All other nitrile oxides formed preferably anti-74. The anti/syn ratio increased from 60 40 (R = P-O2NC6K4) and 65 35 (R = Ph) to 87 13 and 92 8 for bulky ten-Bu and mesityl substituents, respectively. The transition-state structure of the cycloaddition of formonitrile oxide was determined using both HF/6-31G and B3LYP/6-31G methods. The... 

---