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DOI: 10.1055/s-1991-20866
Ruthenium-Catalysed Additions to Alkynes: Synthesis of Activated Esters and Their Use in Acylation Reactions
Publication History
Publication Date:
07 March 2002 (online)
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Enol esters can be obtained in one step by direct addition of carboxylic acids to terminal alkynes in the presence of a ruthenium-phosphine catalyst of type RuCl2(PR3)(arene). The presence of a nucleophilic phosphine allows the addition of the carboxylate group to the substituted alkyne carbon with high regioselectivity. From hex-1-yne or propyne, enol esters can be obtained with a variety of carboxylic acids including N-protected α-amino acids. Alkenylacetylene derivatives are thus precursors of 2-acyloxy-1,3-dienes. Ruthenium-catalysed addition of carboxylic acids and N-protected α-amino acids to propargyl alcohol derivatives gives rise to the synthesis of β-oxopropyl esters. These enol esters and β-oxopropyl esters are shown to be efficient acylating reagents under mild conditions to produce optically active amides or dipeptides. Especially stable enol formates allow access at 25°C to a variety of formamides and α-formylamino esters and in the presence of imidazole as a catalyst, they react with functionalised alcohols to give formates. Enol oxalates are shown to give access to α-dioxo derivatives via acylation of ammonia, amines, and unsaturated alcohols. 1. Introduction 2. Catalytic Synthesis of Enol Esters 2.1. Synthesis of Hex-1-en-2-yl (1-Butylethenyl) Esters 2.2. Synthesis of Isopropenyl (1-Methylethenyl) Esters 2.3. Mechanism of the Catalytic Addition to Terminal Alkynes 2.4. Synthesis of 2-Acyloxy-1,3-Dienes 2.5. Synthesis of β-Oxoalkyl Esters 3. Use of Enol Esters as Acylating Reagents 3.1. Acylation and Dipeptides Synthesis 3.2. Enol Formates as Formylation Reagents 3.3. Enol Oxalyl Esters as Intermediates of α-Dioxo Compounds 4. Conclusion and Perspectives