Photochemische Umwandlungen, 65¹⁾. Die 3σ → 3π‐Route zu 1H‐Azepinen/Benzoliminen

Abstract

Der Substituenteneinfluo auf die einzelnen Schritte der 30-3x-Route zu 1 H-Azepinen wird an Hand mehrerer neu synthetisierter Edukte niiher definiert: Das C-unsubstituierte 7-Azanorbornadien 2a, das 2,3-Dichlorderivat 2 b, der 5,6-Dichlor-2,3-dicarbonester 2c und die an C-l/N-7 mit einem dipolarophilen Rest versehenen 2,3-Dicarbonester 26, e lassen sich durch sensibilisierte/direkte Lichtanregung mehr oder weniger einheitlich in die zum Teil hochlabilen Azaquadricyclane 29 ae isomerisieren. Fur die thermische Umwandlung des Grundgeriistes (N-Tos) 29a werden die kinetischen Parameter bestimmt (Benzol): E, =28.0 f 0.2 kcal/mol, lg A = 15.7; AH* = 27.3 f 0.2 kcal/mol, AS* = 11.1 f 0.7 e.u.Diese Barriere wird durch die Halogenreste in 29b(c) noch starker als durch die Esterreste (290 herabgesetztwobei die +M-im Gegensatz zu den ---Resten ausschlieBlich die Spaltung der gegeniiberliegenden Cyclopropanbindungen bewirken. Die intermediaren Azomethinylide konnen je nach Substitution mit dipolarophilen Reagentien unterschiedlich gut abgefangen werden. Im Fall von 29d (28d) ist die intramolekulare Addition der nichtaktivierten In-Seitenkette (37) bei -30°C so rasch, daB Azepinbildung fast vollstandig unterdriickt wird (Cn2 + 02 + 02], 36?). Das Azepin/Benzolimin-Gleichgewichtsgemisch 31c P 32c (ca. 90: 10) kristallisiert als 31 c (Rontgenstrukturanalyse). Photochemical Transformations, 65 ') The 3a-+fx-Route to lH-Azepines/Benzene IminesWith several newly prepared substrates the influence of substituents upon the individual steps in the 30+3x-route to Iff-azepines is more precisely defined: The C-unsubstituted 7-azanorbornadiene 2a, its 2,3-dichloro derivative 2 b, the dimethyl 5,6-dichloro-2,3-dicarboxylate 2c, and the diesters 2d,e with dipolarophilic groups at C-1/N-7 are selectively isomerized by sensitized/direct photoexcitation into the azaquadricyclanes 29a -e, some of which are highly unstable. For the thermal conversion of the basic skeleton (N-Tos)29a the kinetic parameters have been determined (benzene): E, = 28.0 f 0.2 kcal/mol, Ig A = 15.7; AH* = 27.3 f 0.2 kcal/mol, AS* = 11.1 f 0.7 e. u. This barrier is lowered more efficiently by the chloro (29b,c) than by the methoxycarbonyl substituents (290, with the former (latter) causing exclusive scission of the opposite (neighbouring) cyclopropane bonds. The intermediate azomethine ylides are captured with dipolarophilic reagents more or less efficiently 0 VCH Verlagsgesellschaft mbH, D-

The Reaction of N-Magnesium Derivatives of Pyrroles with N-Mesylchloromethylpyrroles: A Synthesis of Dipyrrylmethanes

“…12 (105 mg, 1.11 mmol) was treated with tosyl chloride (306 mg, 1.60 mmol, 1.4 equiv) as described for the preparation of 14a . The resulting oil was purified by flash chromatography on silica (ethyl acetate/light petroleum, 1:2) to give 14b (272 mg, 99%) as a pink solid: mp 92−94 °C (lit . 94 °C).…”

“…A sample of 14b (82 mg, 0.33 mmol) was reduced with zinc borohydride (2.35 mL of a 0.14 M solution in dry diethyl ether, 0.33 mmol) using the method described for 15a . Purification of the product by flash chromatography on silica (ethyl acetate/light petroleum, 1:2) gave 15b as a pale pink solid (75 mg, 91%): mp 94−96 °C (lit . 97 °C); IR (CHCl 3 ) 3582, 1367, 1175, 1150 cm -1 ; 1 H NMR (CDCl 3 , 300 MHz) δ 2.38 (s, 3H), 2.95 (br s, 1H), 4.59 (s, 2H), 6.21−6.25 (m, 2H), 7.25−7.29 (m, 3H), 7.70 (m, 2H); 13 C NMR (CDCl 3 , 75 MHz) δ 21.4, 56.6, 111.7, 114.9, 123.3, 126.5, 130.0, 134.4, 135.8, 145.1; HRMS calcd for C 12 H 13 NO 3 S 251.0616, found 251.0615.…”

3-Heteroquadricyclanes in organic synthesis

“…Consequently, the synthesis of N-p-tosyl-7azanorbornadiene (9) could only be achieved in moderate yield by a multistep reaction sequence. 14 On the other hand, the photoisomerization 9 -10 is usually performed in the same way as in the oxygen series (high-pressure UV lamp, Pyrex filter, ether as solvent) either by direct or by acetone-sensitized excitation (Scheme 3). Yields as high as 94% (e.g., for 10) have been reported by Prinzbach and co-workers.…”

“…Yields as high as 94% (e.g., for 10) have been reported by Prinzbach and co-workers. 14 The photoreaction and work-up procedures have to be carried out at low temperatures because many azaquadricyclanes are thermally very unstable and undergo isomerization to azepines (see section IV.A,B).…”

A Straightforward Synthesis of 3,4-Difluoropyrrole

“…3,4-Dihalopyrroles have been employed as Diels−Alder dienes, − and as precursors for poly(3,4-dihalopyrroles). ,, In addition, these compounds have been recognized as potential starting materials for selectively or heavily halogenated azamacrocycles . The recently reported class of highly electron deficient β-octachloro- and β-octabromoporphyrins could, in principle, be prepared from the corresponding 3,4-dihalopyrroles, but this approach has been supplanted by the development of efficient methods to chlorinate and brominate the macrocycle periphery. − In contrast, 2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraarylporphyrins have only been successfully synthesized from the condensation of 3,4-difluoropyrrole, 1 , with aryl aldehydes. , Direct fluorination of tetraarylporphyrins gave pigments of a still undetermined structure .…”