Enantioselective Synthesis of Spiropyrazolone-Fused Cyclopenta[c]chromen-4-ones Bearing Five Contiguous Stereocenters via (3+2) Cycloaddition.

An enantioselective synthesis of spiropyrazolone-fused cyclopenta[c]chromen-4-ones is demonstrated via a (3+2) cycloaddition reaction. The reactions of 3-homoacylcoumarins and α,ß-unsaturated pyrazolones in the presence of the cinchona-alkaloid derived hydrogen-bonding catalyst provide aforementioned spiropyrazolone-chromenone adducts bearing five contiguous stereocenters, of which one is the spiro all-carbon quaternary stereocenter in high yields (up to 98%) with good to excellent stereoselectivities (>25:1 dr and up to 99% ee). This one-pot methodology could also be practically demonstrated on a gram-scale with similar efficacy.

Organophosphane-Catalyzed Direct ß-Acylation of 4-Arylidene Pyrazolones and 5-Arylidene Thiazolones with Acyl Chlorides.

An efficient method for the direct ß-acylation of arylidene pyrazolones and thiazolones with acyl chlorides in the presence of a base catalyzed by organophosphanes is reported. A variety of functionalized 4-arylidene pyrazolone and 5-arylidene thiazolone derivatives were prepared under metal-free and mild conditions via a tandem phospha-Michael addition/O-acylation/intramolecular cyclization/rearrangement sequence. Our mechanistic investigations revealed that the reaction is highly stereospecific to provide exclusively cis-isomers, and the methodology can also be scaled up with similar efficacy.

Organophosphane-Promoted Synthesis of Functionalized α,ß-Unsaturated Alkenes and Furanones via Direct ß-Acylation.

We report a phosphine-mediated direct ß-acylation of α,ß-unsaturated 1,3-diketones with acyl chlorides and a base. Functionalized furanones were also prepared by the reaction of cinnamic acid and acyl chloride according to our protocol via ß-acylation. Our studies revealed that α,ß-unsaturated 1,3-diketones with an electron-donating group at the second position favor the formation of ß-acylated products, whereas those with oxygen, such as anhydrides, favor furanones via an unprecedented C-acylation/cyclization sequence.