The structural element of a protonated imidazolium system was realized for the first time in the synthesis of 1 from 2,2'-bipyridine and a novel methylenating agent. Reversible deprotonations proceed via 2 to lead to carbene 3, a formal 1:1 complex between singlet carbon and 2,2'-bipyridine which is stable in solution and can be trapped. For 1 and 2, unusual hybridizations of the bridging C atom were found experimentally.
Das Strukturelement eines protonierten Imidazoliumsystems wurde mit der Synthese von 1 aus 2,2′‐Bipyridin und einem neuartigen Methylenierungsmittel erstmals realisiert. Reversible Deprotonierungen führen über 2 zum in Lösung stabilen und abfangbaren Carben 3, einem formalen 1:1‐Komplex aus Singulett‐Kohlenstoff und 2,2′‐Bipyridin. Für 1 und 2 wurden experimentell ungewöhnliche Hybridisierungen des Brücken‐C‐Atoms gefunden.
R o b ert Weiss*, M atthias H an d k e, Frank H am pelInstitut für O rganische C hem ie I d er F riedrich -A lex an d er U n iversität E rlangen-N ürnberg, H enk estraß e 42, D-91054 E rlan g en , G erm any Z. N aturforsch. 53b, 9 1 6 -9 2 6 (1998); received M arch 11, 1998 G em inal B isonium Salts, SN-R eaction, Synthesis, R egioselectivity, X -R ay D ataare synthetically versatile 1,1-biselectrophiles featuring the sulfonio-and triflato -su b stitu en ts as leaving groups of differential nucleofugic pow er. R eactions with a n u m b er o f n eu tral nucleophiles INu yield a series of novel sulfoniom ethylated onium salts [R 2S -C H 2-N u]2+ 2 0 T f _ 2 -8 u n d er very mild conditions. Structures of salts 2a, 5a and 6b w ere confirm ed by X -ray analysis. W ith certain N -hetarenes exchange of both nucleofuges in la was achieved, yielding the sym m etrical 1,1-bisonium salts 9 and 10. W ith pyridine(derivatives) selective substitu tio n of th e sulfoniofunction in 1,1-bisonium systems 2a and 5a was also realized. These reactions re p resen t typical exam ples of nucleophilic substitutions at gem inally bisonio su b stitu ted Csp3 centers, which we recently have in tro duced as a novel variant of SN2 reactivity.
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1998 substitution reactions substitution reactions O 0040 50 -041 [R 2 S-CH 2 -OTf ] + OTf − as a Reagent with an Optionally Mono-or Biselectrophilic Csp 3 Center. -The sulfonium salts (I) are synthetically versatile 1,1-biselectrophiles featuring the sulfonio-and triflato-substituents as leaving groups. Reactions with a number of neutral nucleophiles yield a series of novel sulfonio-methylated onium salts [cf. (III), (VI)] under very mild conditions. With certain nucleophiles, exchange of both nucleofuges can be achieved providing access to symmetrical [cf. (IV), (IX)] as well as achieved unsymmetrical 1,1-bisonium salts [cf. (IX)]. -(WEISS, R.; HANDKE, M.; HAMPEL, F.; Z. Naturforsch., B: Chem. Sci. 53 (1998) 8, 916-926; Inst. Org.
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