Generation of bicyclo[4.1.0]heptatrienes

Abstract

The reversible Smiles rearrangement between S-(2,4-dinitrophenyl)cysteine (la) and N-(2,4-dinitrophenyl)cysteine (2a) has been kinetically studied in methanol, DMF, and Me^O containing an organic base such as imidazole or DBU. The overall reaction is composed of the spontaneous and base-catalyzed reactions. In methanol the rearrangement from la to 2a goes virtually to completion in most cases. In DMF containing DBU, the reverse rearrangement from 2a to la becomes observable to afford eventually an equilibrium mixture of la and 2a. During this transformation an intermediate was spectroscopically detected, which showed an absorption band around 500 nm. The amide derivative of la (lb) failed to undergo a facile rearrangement except under much severer

Bicyclo[n.1.0]alkenes

“…36 Despite the lack of evidence for cyclopropene intermediates in these reactions, simple bicycloheptatrienes have been generated by dehydrochlorination-isomerization reactions of gem-dichlorocyclopropanes. 32 The bicycloheptatriene generated under the reaction conditions rearranges to the arylcarbene. Products that might arise from ring expansion could not be isolated.…”

Eliminations Involving Carbon–Halogen Bonds and Leading to Highly Strained Rings

“…The corresponding dibromocyclopropane does eliminate at low temperature to give the bromocyclopropene 6, which may be trapped by addition to diphenylisobenzofuran in moderate yield; once again, at higher temperatures the product is 5, X = Br 34,35 . The monochloride 7, R = H is also unreactive to KOBu-t in THF but, despite an earlier report 36 , the addition of DMSO to the solvent mixture does lead to a low yield of a product of addition to the derived cyclopropene 37 .…”

“…In the case of bromides, lithium-bromine exchange in normally preferred to lithiumhydrogen exchange and alternative reactions ensue: The dichloride 17, R = H is dehydrohalogenated to a cyclopropene by addition of nucleophiles such as phenylthiolate but, in the absence of a trap, it ring-opens to a carbene which in turn is intercepted by insertion into the solvent 36,37,85 . In the case of related cyclopropanes e.g.…”

Generation and Trapping of Cyclopropenes from 2‐Alkoxy‐1,1‐dichlorocyclopropanes

“…-With base, I, I-dichlorocyclopropanes react by hydro,chloro-elimination to chlorocyclopropenes which can be intercepted with nucleophiles [ 11 [2] or with furans and isobenzofurans [3] 141. In the absence of trapping agents, they may undergo rearrangements at or below room temperature to vinylcarbenes, which yield cyclopropane adducts with alkenes [4] [5] or products derived from inter-or intramolecular insertion into activated CH bonds [2] [6] [7] (Path A, Scheme I ) . The intramolecular cap- …”