Formal anti-carbopalladation reactions of CC triple bonds are uncommon, but highly useful transformations. Alkynes can be designed to give anti-carbopalladation products. Prerequisite is the exclusion of other reaction pathways to provoke the cis-trans isomerization of the syn-carbopalladation intermediate. Detailed mechanistic studies of this crucial step by experimental and computational means were performed. Application of an intramolecular version for the synthesis of oligocyclic compounds and substituted dibenzofurans is also described.
We investigated [{(Me2NCH2)2(C4H2N)}Li]2 (1) by means of experimental charge density calculations based on the quantum theory of atoms in molecules (QTAIM) and DFT calculations using energy decomposition analysis (EDA).
Rearrangements of furan‐, thiophene‐ and N‐Boc‐pyrrole‐derived donor–acceptor cyclopropanes initiated by Brønsted acids were investigated. Throughout the study, ketones or aldehydes were utilized as accepting moieties and oxygen, sulfur and Boc‐protected nitrogen were used as the donor atoms. Whether a ring‐enlargement and thus an annelation of a five‐membered ring, or a ring‐opening of the three‐membered ring followed by rearomatization to the parent heterocycles takes place strongly depends on the substitution pattern of the cyclopropane. Commonly, more substituted substrates led to annelation whereas less substituted substrates tend to undergo rearomatization. In general, good yields were obtained for starting materials with oxygen and nitrogen donors, whereas the reactions with sulfur as donor gave only poor yields.
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