Peracid induced ring opening of some isoxazolidines and oxidation of saturated 1,3-oxazines to new heterocyclic nitrones

Synthesis of N-substituted 6-trifluoromethyl-1,3-oxazinanes

“…1 H NMR (200 MHz, CDCl 3 ): δ 1.73 -1.76 (m, 4H, H-3), 2.88 -2.98 (m, 8H, H-4, H-7), 3.52 (t, 1H, 3 J H6-H7 6.6 Hz, H-6 ), 3.57 ( t, 1H, 3 J H6'-H7 6.6 Hz, H-6'), 3.68 (s, 6H, -OCH 3 ), 4.05 -4.10 (m, 2H, H-2), 5.14 (br s, 4H, -OH, -NH), 7.11 -7.31 (m, 10H, Ph). 13 …”

“…1 H NMR (200 MHz, CDCl 3 ): δ 1.65 -1.77 (m, 1H, H-5), 1.96 -2.04 (m, 1H, H-5'), 2.57 (s, 3H, H-7), 2.89 -3.00 (m, 1H, H-4), 3.14-3.38 (m, 1H, H-4), 3.84 -3.90 (m, 1H, H-6), 4.28 (d, 1H, J 9.6 Hz, H-2), 4.61 (d, 1H, J 9.6 Hz, H-2'). 13 Data for (6-trifluoromethyl-1,3-oxazinan-3-yl 168 (100), 154 (54), 138 (43), 116 (45), 74 (57). IR (film) ν max /cm -1 : 1748, 1266.…”

“…12 Another method to synthesize 1,3-oxazinanes is by peracid-induced ring opening of isoxazolidines derived from the reaction of nitrones and alkenes. 13 A chiral approach to the synthesis of 1,3-oxazinan-2-ones utilizes aspartic acid as the starting material in a multistep procedure that includes the formation of an epoxide containing a Cbz-protected arylamine as the key intermediate. The synthesis continues with the epoxide ring opening by sodium azide followed by an intramolecular cyclization of the hydroxy group with the benzylcarbamate group to give the desired 1,3-oxazinan-2-one.…”

Asymmetric Reactions

“…In line with earlier results (399,400), oxidation of styrene-derived adduct 350 with m-CPBA facilitated NÀ ÀO cleavage and further oxidation as above to afford a mixture of three compounds, an inseparable mixture of ketonitrone 351 and bicyclic hydroxylamine 352, along with aldonitrone 353 with a solvent-dependent ratio (401). These workers have prepared the analogous nitrones based on the 1,3oxazine ring by oxidative cleavage of isoxazolidines to afford the hydroxylamine followed by a second oxidation with benzoquinone or Hg(II) oxide (402)(403)(404). These dipoles, along with a more recently reported pyrazine nitrone (405), were all used in successful cycloaddition reactions with alkenes.…”

Conversion of Fused-ring Isoxazolidines to α-(Hydroxymethyl)lactones by 3-Chloroperbenzoic Acid

“…Isoxazolidines 1 are becoming popular synthetic intermediates since they (i) can be easily prepared by cycloaddition of nitrones to alkenes and (ii) are prone towards the selective cleavage of the N-O bond under both reductive 2 and oxidative [3][4][5][6][7][8][9][10][11][12][13][14] conditions. In the latter instance, 3-chloroperbenzoic acid (MCPBA) is the most typical reagent and the usual outcome of the oxidation is again a nitrone derivative (the so-called second generation nitrone), which in certain cases recyclizes spontaneously to 1,3-oxazine 3,7,12,13 but can often be used as a 1,3-dipole for further cycloadditions. 4,5,8,9,11 However, it is apparent from the pioneering work of LeBel 3 as well as from a few successive papers [6][7][8][9][10] that appropriate MCPBA treatment of isoxazolidines can furnish the carbonyl compounds formally corresponding to hydrolysis of the initially formed nitrones.…”