Studies On Domino Reactions Involving Benzyne Or Ketenimine

Domino reaction has been highlighted as one of research frontier, and widely applied for the construction of heterocycles in combinatorial chemistry and total synthesis of natural products. In this thesis, domino reactions involving a benzyne or ketenimine intermediate were explored for the synthesis of aromatic rings and heterocycles. The details and results are summarized below:(1) A domino reaction of benzyne,α,β-unsaturated aldehydes and dimethyl benzylphosphonates to 1,4-diaryl-naphthalenes has been developed. The tandem process involves a Wittig-Horner reaction ofα,β-unsaturated aldehydes with benzylphosphonates, a [4+2] cycloaddition of the thus-formed diene with benzyne, and a subsequent dehydrogenation. This simple and efficient approach yields 26 compounds.(2) A domino reaction of 2-azido-2-enoates, arynes and triphenylphosphine to indoles and benzoindoles has been developed. A plausible mechanism for this approach has been proposed as follows:First,2-Azido-2-enoates react with triphenylphosphine to form phosphazenes, while aryne precursors transform to arynes via fluorion effect. Then phosphazenes and arynes undergo a cascade nucleophilic addition, Michael addition, oxidation and 1,3-H shift process to form indoles and benzoindoles. This mild and efficient approach provids 24 compounds.(3) A domino reaction of 2-azido-2,4-dienoates,2-diazocarbonyl compounds and triphenylphosphine to prydines has been developed. The cascade process involves a Staudinger-Meyer reaction, a Wolff rearrangement, an aza-Wittig reaction, and an electrocyclic ring-closure. This general and efficient approach affords 29 compounds.