Deacylative 1,6-addition of Bestmann-Ohira reagent to p-quinone methides for the synthesis of α-diazo-β-diarylphosphonates and cis-stilbenyl phosphonates

• Published in: Tetrahedron 2019-04, Vol.75 (14), p.2246-2253
• Main Authors: Pati, Soumyaranjan, Namboothiri, Irishi N.N.
• Format: Article
• Language: English
• Subjects: 1,6-Conjugate addition; Bestmann-Ohira reagent; cis-Stilbenyl phosphonates; p-Quinone methides; α-Diazo-β-diarylphosphonates
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2019.02.055

The role of Bestmann-Ohira Reagent (BOR) as a conjugate addition partner is reported for the first time. Deacylation of BOR in the presence of ethanolic KOH and 1,6-addition of the resulting diazophosphonate anion to p-quinone methides (PQMs) provides β-disubstituted α-diazophosphonates in good to excellent yields in most cases. Such 1,6-adducts further undergo Rh-catalyzed elimination of the diazo group and 1,2-migration of the phenolic group to afford cis-stilbenylphosphonates with high E-selectivity. The migration of the phenolic group presumably takes place via a spirocyclopropane intermediate derived from the Rh-carbenoid. [Display omitted] •α-Diazo-β-ketophosphonate (Bestmann-Ohira reagent-BOR) takes part in conjugate addition for the first time.•Deacylation of BOR under basic conditions generates the diazophosphonate anion which adds in a 1,6-fashion to para-quinone methides (PQMs).•The 1,6-adduct undergoes Rh-catalyzed transformation to cis-stilbenyl phosphonates.•The above transformation involves Rh-catalyzed elimination of the diazo group and 1,2-migration of the phenolic group.•The 1,2-migration takes place with high E-selectivity through a spiro-cyclopropane intermediate.