Competing [ 2 + 31 and [ 4 + 31 Cycloadditions of C , N - Diphenylnitrone with 1 , 3 - Dienes . Evidence for Thermally Nonequilibrated Intermediatest

at -78 "C for 4 h. To the mixture was added a solution of compound 14 (5.0 mmol) and AlCl, (5.0 mmol) in CH2C12 (15 mL) dropwise. The mixture was stirred at -78 "C for 4 h and allowed to warm to room temperature. The mixture was hydrolyzed with water and extracted three times with ether. The ether phase was washed with brine, dried (MgSO,), and filtered. The filtrate was evaporated and the residue was purified by column chromatography using petroleum ether-ethyl acetate (100:2) as eluent to give 0.87 g of compound 12 (65% yield): [aI2OD = -2.01 (CHCI,); lR (neat) 3090,3070,3030,1715,1140,1100,745; lH N M R (CDCl,) 1.15 (d, J = 6 Hz, 3 H), 1.0-2.2 (m, 6 H), 3.4 (m, 4 H), 3.9 (tt, J = 5, 11.5 Hz, 1 H), 4.4 (s, 2 H), 7.2 (m, 5 H). Anal. Found: C, 67.02; H, 7.85. Calcd for C15H21C102: C, 67.03; H, 7.87. cis-6-Methyl-2-[2-(benzyloxy)ethyl]tetrahydropyran (15). To a mixture of sodium (0.3 g), tert-butyl alcohol (0.5 mL), and ether (10 mL) was added dropwise a solution of compound 12 (0.15 g) in ether (5 mL). The mixture was refluxed for 8 h. The excess sodium was destroyed with methanol and then water (5 mL). The mixture was extracted three times with ether. The ether phase was washed with brine, dried (MgSO,), and filtered. The filtrate was evaporated and the residue was purified with column chromatography using petroleum ether-ethyl acetate (100:2) as eluent to give 0.10 g of compound 15 (76% yield): 'H NMR (CDC1,) 1.1 (d, J = 6 Hz, 3 H), 1.0-1.8 (m, 8 H), 3.4 (m, 4 H), 4.4 (s, 2 H), 7.2 (m, 5 H); MS 234 (15), 216 (20), 143 (35), 107 (60), 99 (85), 77 (l), 28 (100). (2R ,6R )-(-)-(cis-6-Methyltetrahydropyran-2-yl)acetic Acid (11). Compound 15 (0.10 g) was hydrogenolyzed in ethanol (5 mL) with P d C (O.Os0 g) under hydrogen (2 atm) for 40 h. The catalyst was removed by filtration and the filtrate was evaporated. The residue was dissolved in acetone (5 mL). To the acetone solution was added Jones reagent (3 mL) dropwise. The mixture was stirred at room temperature for 1 h. The excess oxidant was destroyed with 2-propanol (2 mL) and the mixture was extracted with ether. The organic phase was washed with brine twice, dried (MgSOJ, and filtered. The filtrate was evaporated and the residue was purified by column chromatography to give 0.052 g of compound 11 (77% yield): [aIz1D = -5.47' (CHC1,) [lit.% [aIz2D = +18.6" (CHCI,)]. The spectroscopic data of 11 were in agreement with those reported in the literature.20