Summary1,2exo-Diiodo-norbornane (4) was prepared from norcamphor hydrazone by oxidative iodination and subsequent rearrangement of the 2,2-diiodo-bicyclo [2.2. llheptane (2). The stable a-iodohydrazone 11 was obtained from 1 -iodo-bicyc-10[2.2. IIheptan-2-one (lo), which itself was prepared from I-iodo-norbornene (5). Subsequent treatment of 11 with iodine lead to 1,2,2-triiodo-norbornane (12) and 1,2-diiodo-norborn-2-ene (13). 1,2endo-Diiodo-norbornane (14) was obtained by stereoselective reduction of 12 with tributyltinhydride or by reaction of 13 with diimide.One of the well-established methods for the preparation of bridgehead olefins is the reductive bisdehalogenation of appropriate dihalides [ 11. This procedure was particularly successful for the generation of Ai.2-norbornene [2]. In the course of further transformations and mechanistic investigations of these reductive bisdehalogenations, the two configurational isomers of 1,2-diiodo-norbornane were needed. We now describe the preparation of 1,2exo-diiodo-norbornane (4) and 1,2 endo-diiodonorbornane (14) in detail.Results and discussion. -As reported previously 1,2exo-diiodo-norbornane (4) had been obtained from the hydrazone of norbornan-2-one (1) [2]. The key step in this preparation is the oxidation of the hydrazone of 1 with iodine in the presence of a base (Barton-Sternhell reaction) [3] which leads to a mixture of 2,2-diiodo-norbornane (2) and 2-iodo-norborn-2-ene (3). In variance with the published procedure, a mixture of hydrazone and triethylamine was added to a solution of iodine in benzene. However, these inverse reaction conditions had no significant effect on yield and ratio of 2 and 3.Lewis-acid catalyzed rearrangement of 2 gave 4 in 42% yield (over two steps). The structure of this compound was established by transformation into the known I-iodo-norbornane (6) via 1-iodo-norbornene (5) [4] (cf. Scheme 1).
SummaryReductive elimination at 1,2exo-diiodonorbornane (6) was induced by Collman ' s reagent. Surprisingly, 1,2endo-diiodonorbornane (9) and l-iodo-2endo-trifluoromethylsulfonyloxy-norbornane (lob) lead only to reactions of the substituent in 2-position. Mechanistic aspects are related to the reactions of monosubstituted iodonorbornanes with Collman's reagent.Einleitung. -Nach wie vor ist die Reaktivitat von d'.*-Norbornen (1) weitgehend unbekannt. Dies hangt vor allem damit zusammen, dass das hoch reaktive BredtOlefin 1 [l] im Gegensatz zu Bicyclo
Norcampherhydrazon (Ia) wird mit Iz/Benzol zum (nichtisolierten) Diiodid (Ib) [daneben die Verbindung (II)] umgesetzt, das durch Lewissäure‐katalysierte Umlagerung das Diiodid (III) liefert.
Bei der Reaktion des exo‐Diiodnorbomans (Ia) mit Collmans Reagenz (II) in einem Gemisch von THF/Methylpyrrolidon/Furan (III) bei tiefer Temp. entstehen die Furanaddukte (IV) und (V); daneben werden die Verbindungen (VI) und (VII) sowie Spuren von (VIII) gefunden.
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