196952-91-7Relevant academic research and scientific papers
Isomerizations on silica gel: Synthesis of allenyl ketones and the first Nazarov cyclizations of vinyl allenyl ketones
Stephen,Hashmi,Bats, Jan W.,Choi, Ji-Hyun,Schwarz, Lothar
, p. 7491 - 7494 (2007/10/03)
Dess-Martin oxidation followed by the chromatographic workup of crude, terminal propargyl ketones 5 on silica gel directly leads to terminal allenyl ketones 6. When the other substituent on 5 was electron-rich, 7 was observed as side-product. If the other substituent on 5 was electron-poor, the isomeric 1-propynyl ketone 8 was the side-product. Chromatography of the crude propargyl vinyl ketones 10 on silica gel delivers the products of a Nazarov cyclization.
C-C-Bond Formation by the Palladium-Catalyzed Cycloisomerization/Dimerization of Terminal Allenyl Ketones: Selectivity and Mechanistic Aspects
Hashmi, A. Stephen K.,Ruppert, Thorsten L.,Knoefel, Thomas,Bats, Jan W.
, p. 7295 - 7304 (2007/10/03)
The scope of the palladium-catalyzed cyclization/dimerization of terminal allenyl ketones 1 to the 2,4-disubstituted furans 3 has been investigated. Simplified and improved conditions almost exclusively provided the dimer 3, accompanied by only traces of the easily separable monomer 2. The formation of an isomer of 3, the unconjugated ketone 4, was completeley suppressed. Under these mild conditions, besides the normal functional group tolerance known for palladium-catalyzed reactions, an interesting selectivity was observed with functional groups that are known to react either in palladium-catalyzed reactions or reactions catalyzed by other transition-metals. Thus aryl halides, terminal alkynes, 1,6-enynes, and α-allenic alcohols were tolerated. In the latter example the selective reaction of only one out of two different allenes was achieved. Mechanistic investigation indicated a Pd(II)/Pd(IV)-cycle involving palladium(II)-γ-alkoxyvinylcarbene and furylpalladium(IV) hydride intermediates, although a second pathway for the formation of the dimer 3 which also involves Pd(IV)-intermediates like the 3,4-dimethylenepalladacyclopentane 23 and the 3-methylenepalladacyclobutane-like structure 15 (respectively 25) could not completely be excluded.
