Base- and sulfur-promoted oxidative lactonization of chalcone-acetate Michael adducts: access to pyran-2-ones

A cost-effective, practical, straightforward and scalable synthesis of α-pyrones via base- and sulfur-promoted annulation of phenylacetates and chalcones is reported. Generated in situ from the starting components by using dbu as a base catalyst, the Michael adducts underwent a smooth oxidative cyclization into 3,4,6-triaryl-2-pyranones upon heating with DABCO and sulfur in DMSO. Extension to malonate in place of phenylacetates led to 4,6-diaryl-2-pyranone-2-carboxylates.

Selenium-promoted electrophilic cyclization of arylpropiolamides: synthesis of 3-organoselenyl spiro[4,5]trienones

This paper describes a selenium-promoted electrophilic cyclization of arylpropiolamides allowing the synthesis of 3-organoselenyl spiro[4,5]trienones via a 5-endo-dig ipso-mode. The 3-organoselenyl-quinolinone derivative formation via 6-endo-dig was avoided using an electrophilic organoselenium species in a metal-free protocol. The use of phenylselenyl bromide (1.3 equiv.), as the electrophilic source, in nitromethane (3 mL) at 90 °C enabled the cyclization of N-(2-methoxyphenyl)-N-methyl-3-phenylpropiolamides, giving 3-organoselenyl[4,5]triene-2,6-dione derivatives. The extension of the standard conditions to the N-(4-methoxyphenyl)-phenylpropiolamides led to the corresponding 3-organoselenyl spiro[4,5]trienones having the carbonyl group at the 8-position. Besides, we demonstrated a general application of our approach by using 3-organoselenyl spiro[4,5]trienones as substrates in Suzuki cross-coupling reactions, which gave the cross-coupled products in good yields.

Selenolactams as Synthetic Intermediates for the Synthesis of Polycyclic Amines via Seleno-Claisen Rearrangements

A highly diastereoselective α-allylation of selenolactams with allyl halides is reported. DFT analyses and experimental observations suggested that this reaction proceeds via a Se-allylation of the eneselenolates of the lactams followed by a seleno-Claisen rearrangement. The thus-obtained products could be efficiently transformed into polycyclic amines using a previously developed sequential addition of organometallic reagents and ring-closing metathesis.