4,5-Dihydro-1H-azepine aus aktivierten Cyclobutenen und 1,3-Dipolen

Das 7-Oxanorbornadien-Grundgeriist @a), das 2,3-Bis(trifluormethyl)-Derivat (8 b) und diverse 2,3-Dicarbonester mit potentiell dipolarophilen Gruppen an C-1 (16a -d, 17a-c) wurden synthetisiert und durch sensibilisierte (8a, b) bzw. direkte Lichtanregung (16a-d, 17a-c) durchweg hochselektiv in die 3-Oxaquadricyclane (18a, b, 19a-d, 20a-c) umgewandelt. Bei der Thermolyse dieser Oxaquadricyclane [18a(b): E.(C6Ds) = 32.6 & 0.3 kcal/ mol (32.2 5 1.4 kcal/mol); Ig A = 15.8 (14.5)] begunstigen CF3(CH3C02)-Reste an C-2(3) die Spaltung der gegeniiberliegenden (benachbarten) Cyclopropanbindungen. Durch Konkurrenzversuche mit Acetylendicarbonsaure-dimethylester als externem Dipolarophil wird der Mehrstufen-Mechanismus der Oxaquadricyclan -+ Oxepin-Isomerisierung untermauert. Die intramolekulare Carbonylylid-Abfangreaktion kann in 19a -d nicht, wohl aber in 20a-c mit der Oxepinbildung konkurrieren. Deren im Falle von 20a auBergewohnlich niedrige Aktivierungsbarriere (E,(C6D6) = 23.5 f 1 kcal/mol; Ig A = 11.6) und singulare Spezifitlt werden im Sinne einer konzertierten [%2 + ,2 + ,2]-Cycloaddition an die Bishomofuran-Einheit des Oxaquadricyclan-Geristes interpretiert. Photochemical Transformations, 64 ') The 3a-+ 3x-Route to Oxepines/Benzene Oxides The 7-oxanorbornadiene skeleton @a), its 2,3-bis(trifluoromethyl) derivative (8b), and several 2,3-dicarboxylic esters with potential dipolarophilic groups at C-I (16a -d, 17a -c) were synthesized and selectively transformed into the 3-oxaquadricyclanes (Ha, b, 19a -d, and 2Oa-c) through sensitized (8a, b) or direct (16a-d, 17a-c) photoexcitation. In the thermolysis of these oxaquadricyclanes [l8a (b): Ea(C6D6) = 32.6 & 0.3 kcal/mol(32.2 & 1.4 kcal/ mol); Ig A = 15.8 (14.5)] CF3(CH3CO2) substituents at C-2(3) favor the scission of the opposite (neighbouring) cyclopropane bonds. Competition experiments with dimethyl acetylenedicarboxylate as external dipolarophile support the stepwise mechanism of the oxaquadricyclane -P oxepine conversion. The intramolecular carbonyl ylide-interception cannot compete with oxepine formation in 19a-d but is efficient in 2Oa-c. The unusually low activation barrier (Ea(C6D6) = 23.5 5 1 kcal/mol; Ig A = 11.6) and singular specifity in case of 2Oa is interpreted in terms of a concerted [%2 + ,2 + ,2]-cycloaddition to the bishomofuran unit of the oxaquadricyclane skeleton. Die nachstehend skizzierte Ringaufweitung von Furanen zu Oxepinen/Benzoloxiden'' und von Pyrrolen zu Azepinen/Benzoliminen3' ist praparativ vielfach ge-0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986 0009 -2940/86/0202 -0589 $ 02.50/0 Chem. Ber. 119 (1986) Photochemische Umwandlungen, 64 H. Prinzbach et al. 21 2 2 J 1 H 0-H 24 25 Chem. Ber. If9 (1986)

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Sulfonyl‐Activated Cyclobutenes as Building Blocks for the Synthesis of Dihydrodiazepines

Landen

Martin

Steigel

1987

Chem. Ber.

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1,2-Bis(phcnylthio)-I-cyclobutcnc (S), prepared in high yield using a modified literature procedure, was oxidized to the corresponding his-sulfone 2. sulfone-sulfoxide 9, bis-sulfoxide 10, or monosulfoxidc 15 by means of hydrogen peroxide or sodium periodate, rcspectivcly. When treated with diazomethane the bis-sulfone 2 and thc sulfonc-sulroxidc 9 yicld thc dihydrodiazcpincs 4 a and 11, rcspcctivcly. Thc rcactivity of thcse cyclobutenes and thc rcgioselectivity of 9 is discussed in terms of the MNDO model.Vinyl sulfoxides and vinyl sulfones are often used as dienophiles because of their high reactivity2). Further activation can be achieved with 1,2-bis(phenylsulfonyl)ethylenes3~. Therefore, these olefins represent useful synthetic equivalents for acetylene4). The activating influence of the sulfonyl group also becomes noticeable in dipolar cycloadditions 5), By inserting a sulfonyl group into the cyclobutene ring a considerable increase of the reactivity of the cyclobutene double bond is achieved. Thiete 1,l-dioxide (1) possesses excellent dienophilic6) and dip~larophilic~) properties. We showed that cycloadducts of cyclobutenes and 1,3-dipoles represent potential precursors to dihydroazepines8) and dih ydrodia~epines~).However, the ring enlargement of dipolar cycloadducts of thiete 1,l-dioxide (1) leading to seven-membered heterocycles has not succeeded yet, Either the adducts eliminate 502'' or the cycloadduct of 1 reacts by splitting the SO2-C bond lo).According to our experience, keto groups in or methoxycarbonyl-and cyano groups at the four-membered ring favour the ring enlargementsx9).In order to examine how much the sulfonyl group facilitates the fission of the central cs bond of the cycloadducts Sulfonyl-aktivierte Cyclobutcne als Synthesebausteine fur die Sjnthese von Dihydrodiampinen " 1,2-Bis(phcnyIthio)-l-cyclobutcn (S), das nach cincm modifizicrtcn Litcraturverfahren in hoher Ausbcutc crhalten wurde, konntc mittels Wasserstoffperoxid byw. Natriumperiodat zum entsprechenden Bis-sulfon 2, Sulfon-sulfoxid 9, Bis-sulfoxid 10 oder Monosulfoxid 15 oxidiert werden. Mit Diazomethan ergeben das Bissulfon 2 und das Sulfon-sulfoxid 9 die Dihydrodiazepine 4a bzw. 11. Die Reaktivitat dicscr Cyclobutcne und die Regiosclcktivitit von 9 wcrdcn im Rahmcn dcs MNDO-Modells diskuticrt.of cyclobutenes (without competing cleavage of an outer bond of the four-membered ring), the preparation of bicyclic pyrazolines 3 with activating phenylsulfonyl substituents and their possible ring enlargement leading to 4 was investigated. We now report on the synthesis of 1,2-bis(phenylsulfony1)-1 -cyclobutene (2) and its reactivity towards diazoalkanes. ResultsThe bis-sulfide 5"), described by Cohen et al., should be a suitable starting material for the sulfone 2. However, the published yield of 70% for 5 could not be reproduced. With sec-butyllithium in THF at -78 "C mixtures of 5 and 8 were obtained (yields: ca. 50% of 5, 30% of 8).We assume that 8 arises from 1,l -bis(phenylthio)ethylene (7) which originates from 6 by Grob fragment...

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4,5-Dihydro-1H-azepine aus aktivierten Cyclobutenen und 1,3-Dipolen

Cited by 11 publications

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Dihydroazepines

Dihydroazepines

Photochemische Umwandlungen, 64. Die 3σ → 3π‐Route zu Oxepinen/Benzoloxiden

Sulfonyl‐Activated Cyclobutenes as Building Blocks for the Synthesis of Dihydrodiazepines

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