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...
