First general approach to cyclohex-3-ene-1,1-bis(phosphonates) by Diels-Alder cycloaddition of tetraethyl vinylidenebis(phosphonate) to 1,3-dienes.
Tetraethyl vinylidenebis(phosphonate) (VBP) reacts smoothly with substituted 1,3-dienes at 90-110 degrees C without solvent to give the corresponding cyclohex-3-ene-1,1-bis(phosphonates) in good yields (60-85%). With nonsymmetrically substituted dienes, mixtures of regioisomers are obtained, the regioisomeric ratio being exclusively controlled by electronic effects. Danishefsky's diene allows tetraethyl 4-oxocyclohex-2-ene-1,1-bis(phosphonate) to be obtained in an 81% overall yield after the acid-catalyzed hydrolysis of the Diels-Alder cycloadduct. With 2,3-dimethoxy-1,3-butadiene, a mixture of regioisomeric dimethoxycyclohexene-1,1-bis(phosphonates) is formed by the VBP-catalyzed isomerization of the normal Diels-Alder cycloadduct. The mixture converges into tetraethyl 3,4-dimethoxycyclohex-2-ene-1,1-bis(phosphonate) at prolonged reaction times.
Ruzziconi
Renzo
R
Dipartimento di Chimica, Università di Perugia, Via Elce di Sotto, 8 I-06123 Perugia, Italy.
Ricci
Giacomo
G
Gioiello
Antimo
A
Couthon-Gourvès
Hélène
H
Gourvès
Jean-Philippe
JP