Ni(NHC) Catalyzed Rearrangement of 1‐Acyl‐2‐vinylcyclopropanes: Tackling a Mechanistic Puzzle by Combined Experimental and Computational Studies

Abstract

The Ni(NHC) catalyzed rearrangement of 1‐acyl‐2‐vinylcyclopropanes to the corresponding 4‐acyl‐cyclopent‐1‐enes is highly promising for the synthesis of keto‐functionalized annelated bi‐ and tricyclic subunits of natural products. Therefore, we investigated the catalytic activity of Ni(NHC) complexes in the rearrangement of 1‐acyl‐2‐vinylcyclopropanes with different ring sizes and substitution patterns. Surprising effects regarding substrate scope and stereoselectivity of the Ni(NHC) catalyzed vinylcyclopropane‐cyclopentene rearrangement were observed. Only vinylcyclopropanes with 1‐methyl, 1‐phenyl, 1,2‐dialkyl or 2‐phenyl‐substitution at the vinyl moiety could be rearranged successfully. Moreover, an endo‐configuration on the cyclopropane ring was required for successful rearrangement. By treatment of the vinylcyclopropanes with Rh catalysts or Lewis acids, the involvement of Lewis acid catalysis could be ruled out. In order to understand these experimental results and to rationalize the reactivity of the Ni(NHC) complexes computational studies were performed, which provided insights into mechanistic details.

Adventures and Detours in the Synthesis of Hydropentalenes

“…On the other hand, vinylcyclopropanes 135a and 135b with a terminal substituted C=C double bond were obtained in decent yields, but unfortunately reacted only sluggishly to give the bicyclo[3.3.0]octenes 134 (Scheme 35). 90 Computational studies confirmed the experimental results. Note that only endo-vinylcyclopropanes endo-135c and endo-135d were reactive in the Ni catalysis, whereas the exo-vinylcyclopropanes exo-135c and exo-135d remained completely unreactive.…”

“…The most annoying side reaction was the [2,3]-sigmatropic rearrangement, resulting in the formation of -allyl sulfides rather than vinylcyclopropanes. 89,90 Despite these disadvantages this approach delivered the desired vinylcyclopropanes 135 in two steps (Route B, Scheme 34), whereas the corresponding Cu-catalyzed…”

“…The required vinylcyclopropanes 135 might come from cyclopentenone and allylsulfonium salts 136 (Scheme 33). 89,90 The synthesis of the vinylcyclopropanes was found to be strongly dependent on the substitution pattern. For example, terminally substituted sulfonium salts (R 2 ≠ H) gave higher yields than vicinally substituted salts (R 1 ≠ H).…”

Remote Fluorination of α,β‐Unsaturated Carbonyls via Silyl Dienol Ethers

“…The authors have cited additional references within the Supporting Information (Ref. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]).…”

Remote Fluorination of α,β-Unsaturated Carbonyls via Silyl Dienol Ethers

“…The authors have cited additional references within the Supporting Information. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]…”