[4+2] Cycloaddition reactions of o-thioquinones with pentafulvenes: efficient synthesis of benzoxathiins

[4+2] Cycloaddition Reactions of β-Naphtha-1-thioquinones Generated from 2-Naphthols and DAST

An original and facile method for the generation of β-naphtha-1-thioquinone using DAST and 2-naphthol has been developed. A series of dehydro-2-naphthol-1-sluphides or naphtha-oxathiane derivatives were synthesized by in-situ Diels-Alder cycloaddition...

Visible-light-induced [4 + 2] cycloaddition of pentafulvenes by organic photoredox catalysis

We have developed thioxanthylium photoredox catalyzed [4 + 2] cycloaddition of pentafulvenes at room temperature under green light irradiation, which affords tetrahydrocyclopenta[b]chromenes with high regioselectivities. The present reaction provides a sustainable approach to carry out the cycloaddition of pentafulvenes without the use of transition metal catalysts or high-temperature conditions. This procedure enables a mild and straightforward access to 1,3a,9,9a-tetrahydrocyclopenta[b]chromenes. The quantum yield of the reaction (Φ = 0.15) indicates that the reaction would mainly proceed via photocatalytic pathways.

An efficient asymmetric synthesis of an estrogen receptor modulator by sulfoxide-directed borane reduction

An efficient asymmetric synthesis of a selective estrogen receptor modulator (SERM) that has a dihydrobenzoxathiin core structure bearing two stereogenic centers is reported. The stereogenic centers were established by an unprecedented chiral sulfoxide-directed stereospecific reduction of an alpha,beta-unsaturated sulfoxide to the saturated sulfide in one step. Studies to elucidate the mechanism for this reduction are reported. Highly efficient Cu(I)-mediated ether formation was used to install the ether side chain, and selective debenzylation conditions were developed to remove the benzyl protecting groups on the phenols.