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A general and convenient method for the synthesis of 2-(hydroxyalkyl)-5-methylenecyclopentenones through the Morita-Baylis-Hillman reaction of a masked 5-alkylidene-2-cyclopentenone followed by the flash vacuum pyrolysis of the resulting adduct is described.

Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3-methyl-3-en-2-one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron-poor bidentate BIPHOP-F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD2Cl2. The results were compared to solid-state structures and to the facial selectivities of catalytic asymmetric Diels-Alder reactions with cyclopentadiene. X-Ray structures of four Ru-enal and Ru-enone complexes show the α, β-unsaturated C=O compounds to adopt an anti-s-trans conformation. In solution, enals assume both anti-s-trans and anti-s-cis conformations. An additional conformation, syn-s-trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti-s-trans conformation, whereas with enones, the major product results from the syn-s-trans conformation. The alkene in s-cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn-s-trans conformation is found in the solid state of the bulky 6,6-dimethyl cyclohexanone-Ru(II) complex. The X-ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η2 bond to one of the alkene moieties. In solution, coordination to Ru-C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids. [ABSTRACT FROM AUTHOR]

The reaction of masked 5-alkylidene-2-cyclopentenones with aldehydes catalyzed by tributyiphosphine in the presence of phenol provided the corresponding Morita-Baylis--Hiliman adducts, which were subjected to flash vacuum pyrolysis to afford 5-alkylidene-2-(hydroxyalkyl)-2-cyclopentenones. [ABSTRACT FROM AUTHOR]

Chiral single-point binding ruthenium Lewis acid catalysts [Ru(acetone)((S,S)-BIPHOP-F)(Cp)][SbF6] ((S,S)-1a) and [Ru(acetone)((S,S)-BIPHOP-F)(indenyl)][SbF6] ((S,S)-1b) efficiently catalyze intramolecular Diels-Alder (IMDA) reactions of trienals under mild conditions to afford the endo cycloaddition products as the major products in good yields with high diastereo- and enantioselectivities.

Single point binding ruthenium Lewis acid catalysts [Ru(acetone)(S,S)-BIPHOP-F)Cp][SbF(6)] ((S,S)-1b) and [Ru(acetone)(S,S)-BIPHOP-F)(indenyl)][SbF(6)] ((S,S)-1c) efficiently catalyze intramolecular Diels-Alder (IMDA) reactions under mild conditions to afford the endo cycloaddition products as the major product in excellent yields with high diastereo- and enantioselectivities.