925423-92-3Relevant academic research and scientific papers
Organocatalytic asymmetric direct α-alkynylation of cyclic β-ketoesters
Poulsen, Thomas B.,Bernardi, Luca,Aleman, Jose,Overgaard, Jacob,Jorgensen, Karl Anker
, p. 441 - 449 (2007/10/03)
The first organocatalytic enantioselective direct α-alkynylation of β-ketoesters and 3-acyl oxindoles is described. It is demonstrated that activated β-halo-alkynes undergo nucleophilic acetylenic substitution catalyzed by chiral phase-transfer compounds to afford the alkynylated products in high yields and excellent enantioselectivities. The potential of the reaction is first demonstrated for various alkynylating reagents having chloride and bromide as the leaving groups and substituents such as allyl and alkyl esters, amides, ketones, and sulfones. These reactions proceed with 74-99% yield and 88-97% ee. Then the scope in nucleophile is demonstrated for a large number of cyclic β-ketoesters with various ring-sizes and for oxindoles as well. The corresponding optically active products are formed in high yields and with enantioselectivities up to 98% ee. The procedure allows for the stereocontrolled attachment of an ethynyl unit in the α-position to the carbonyl compound by facile removal of the activating group, and this has been demonstrated for a number of the optically active allyl esters. Furthermore, the synthesis of optically active 1,4-enynes is also shown. The isolation and characterization by X-ray analysis of the catalyst with p-nitrophenolate as the counterion allowed us to propose a model of the catalyst-substrate intermediate which might account for the observed enantioselectivity of the organocatalytic enantioselective α-alkynylation reaction. Furthermore, it is suggested that this intermediate is also the reactive species for a number of other electrophiles adding to β-ketoesters giving enantioselectivities in the range of 90-98% ee.
The Synthesis of Some Thiophenophanes and Attempted Cyclisations to Polycyclic Thiophenium Salts
Acheson, R. Morrin,Lee, Gary C. M.
, p. 2321 - 2332 (2007/10/02)
5,10-Diphenylcyclotrideca-2,4,10,12-tetraene-6,8-diyn-1-one (28), 5,6,7,8-tetrahydrodibenzocyclotridecen-15-one (21), and 13,14,16,17-tetrahydro-5,6,7,8-tetradehydrodibenzocyclotridecen-15-one (40) were synthesized.All attempts to add hydrogen sulphide across the triple bonds of these compounds to give thiophenes failed. 13,14,16,17-Tetrahydro-5,8-epithiodibenzocyclotridecen-15-one (43), from which hydrogen sulphide was removed by DDQ or chloroanil to give the ketone (40), was synthesized via the copper(II) acetate oxidation of 1,5-bis(2-ethynylphenyl)pentan-3-one (36).This ketone was obtained from 2-iodobenzaldehyde which on successive treatment with acetone, and ethynyltrimethylsilane yielded 1,5-bis(2-trimethylsilylethynylphenyl)penta-1,4-dien-3-one (18).Tributyltin hydride reduced the vinyl double bonds only in this ketone, and subsequent hydrolysis gave the ketone (36).Reduction of the cyclic ketone (40) with sodium borohydride gave the alcohol (41), sodium sulphide converted the diyne grouping into a thiophene ring giving the thiophene alcohol (42), and chromic acid now yielded the ketone (43).Attempts to convert this alcohol (42) and ketone (43) into pentacyclic sulphonium salts or related compounds resulted in elimination of oxygen and the formation of olefins.
