Photochemical transformations of small ring heterocyclic compounds. XLII. 1,3-Dipolar cycloaddition reactions of the azomethine ylide derived from the 1,3-diazabicyclo[3.1.0]hex-3-ene system

Abstract

4, hex-3-ene reacts stereospecifically with dimethyl maléate and dimethyl fumarate in refluxing xylene or on irradiation to give A2-pyrrolines as cycloadducts. The base-catalyzed epimerization of the various adducts supports the stereochemical structure assignments. A likely mechanism for these additions is the conversion of the diazabicyclo system into an azomethine ylide, which subsequently reacts with the unsaturated substrate. The photochemical results imply that the opening of the aziridine ring proceeds by a conrotatory motion in contrast to the disrotatory motion predicted from orbital symmetry considerations. Three possible explanations to account for these results are presented.Cyclopropyl anions are predicted by Woodward and Hoffmann to open thermally to allyl anions by a conrotatory course.3 To date, no clear-cut example of this electrocyclic process is known.4 However, Huisgen and coworkers have recently established that the thermal ring cleavage of the isoelectronic aziridine system proceeds by conrotatory motion.5 The azomethine ylide formed can undergo subsequent 1,3-dipolar cycloaddition with homo and hetero multiple bonds to give a variety of heterocyclic rings.6-10 It has also been found that irradiation of aziridines11-14 and oxiranes15-17 frequently yields products derived from related 1,3-dipole intermediates. These reactions may be envisioned as electrocyclic processes proceeding by disrotatory ring opening.As part of a broad program on the photochemical transformation of small ring heterocycles,18 we recently described some characteristics of the 1,3-diazabicyclo-

1,3-Dipolar cycloaddition reactions of azomethine ylides with aromatic dipolarophiles

“…61 The thermal or photochemical cleavage of aziridines is a well known source of azomethine ylides that undergo 1,3-dipolar cycloaddition reactions. [62][63][64] Tsuge and coworkers found that 4-isoxazolines can be used as precursors of azomethine ylides in 1,3-dipolar cycloaddition reactions and exemplified this via intramolecular addition to a pendant furan ring. 56 The reaction of N-methylnitrone 41a with dimethyl acetylenedicarboxylate…”

Chemistry of .alpha.,.alpha.'-bis(diazo)ketones

“…11: mp 1 19-120°( lit. 119°,56 120-121 °);59 ir (CHC13) 2600-3400 (CQ2H), 1680 (C=0), 1630 (C=C); nmr (CDC13) 11.22 (broad s, 1 H, C02H), 6.95 (m, 1 H, C=CH), 2.60 (t, J = 6.8 Hz with further splitting, 4 H, CH2C=C), 2.20 (distorted quintet, J = 6.8 Hz, 2 H, CH2C/y2CH2); mass spectrum m/e (%) 40 (30), 41 (97), 43 (26), 44 (24), 55 (29), 65 (34), 66 (60), 67 (100), 69 (28), 94 (25), 112 (86), 1 13 (6).…”

“…12: mp 89-90°; ir (CC14) 1775, 1710 (CO-O-CO), 1625 (C=C); nmr (CC14) 6.95 (broad s, 1 H, C=CH), 2.55 (m, 4 H, CH2C=C), 2.10 (m, 2 H, CH2C//2CH2); uv (95% ethanol) 220 (< 10,000); mass spectrum m/e (%) 41 (34), 67 (43), 95 (100), 178 (7); 206 (-0.01); exact mass (caled for Cl2H1403, 206.09429) 206.09367 ± 0.00338.…”

“…7.40 (m, 8 H, Ar-H). 4.36 (m, 2 H, C=C-CH2N), 2.70 (AB q. J = 17.1 Hz, 2 H. C=C-CH2-C), 1.63 (m, 6 H, CH3); uv (95% ethanol) 268 (e 17,600), 390 (3500): mass spectrum m/e (%) 40 (28), 41 (38), 43 (22), 44 (26), 55 (22), 67 (36), 81 (17), 82 (100), 103 (38), 121 (15), 123 (20), 178 (91). 179 (16), 199 (17), 200 (23), 202 (29), 222 (21), 316 (12).…”

“…14): cell dimensions (least-squares refinement using reflections measured at ±9) a = 10.976 (I), b = 7.135 (1), c = 19.740 (1) A; ß = 90. 43 (1)°: V = 1546 A3; Z = 4; d% -1.294 g/cc: dm = 1.28 (1) g/cc (flotation in aqueous KI): radiation. Cu Ka (graphite monochromator, 1.5418 A); µ 4.69 cm-1; crystal habit, monoclinic prismatic elongated along b; diffractometer, Nonius CAD4; crystal size for data collection, 0.125 X 0.150 X 0.570 mm.…”