The Schöllkopf chiron and transition metal mediated reactions, a powerful combination for stereoselective construction of cyclic α-quaternary-α-amino acid derivatives
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The focus has been on the development of methodology for stereoselective preparation of spiroannulated intermediates of the Schöllkopf chiron and further transformations to cyclic α-amino acids. The spiroannulations are effected by Ru(II)-catalysed ring-closing metathesis reactions, by Ru(II)- and Pd(0)-catalysed cycloisomerisations, by Rh(II)-carbenoid cyclisation reactions and by intramolecular aldol condensations. Hydrolytic reactions of the spirane intermediates have provided several groups of highly novel and functionalised five-, six- and seven-membered cyclic α-quaternary-α-amino acid derivatives as well as alicyclic derivatives. The novel cyclic amino acid derivatives can be regarded as cyclic constrained analogues of corresponding common amino acids, or in some cases as intermediates for further preparation of such amino acids. Some emphasis has been on the preparation of cyclic serine analogues. Major efforts have been on the preparation of cyclic α-quaternary bis(α-amino acid) derivatives as conformationally constrained dicarba-analogues of cystine.
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