Asymmetric Diels–Alder cycloaddition of a di-P-stereogenic dienophile with cyclopentadiene

The Diels–Alder cycloaddition of the di-P-stereogenic dienophile (SP,SP)-1 leads to novel di-P-stereogenic norbornene derivatives and proceeds with moderate diastereoselectivity in the absence of a catalyst. In the presence of TiCl4, however, the diastereoselectivity was raised to 9:1. The major diastereoisomer has been characterized crystallographically. The separation of the diastereomeric cycloadducts was possible by fractional crystallization in the presence of (−)-O,O-dibenzoyltartaric acid monohydrate.

Graphical abstractThe asymmetric Diels–Alder cycloaddition of the enantiopure di-P-stereogenic dienophile (SP,SP)-1 in the presence of 0.5 equiv of TiCl4 gives cycloadduct (SP,SP,2R,3R)-2 in 87% yield and 80% de.Figure optionsDownload full-size imageDownload as PowerPoint slide

(SP,SP)-(−)-(E)-1,2-Bis(methylphenylphosphinoyl)etheneC16H18P2O2Ee 98%[α]D20=-255.0 (c 1, CH2Cl2)Source of chirality: resolution of precursorAbsolute configuration: (SP,SP)

(SP,SP,5R,6R)-endo-5-exo-6-Di(methylphenylphosphanoyl)bicyclo[2.2.1]hept-2-eneEe 98%, de 96%[α]D20=-83.5 (c 0.69, CHCl3)Source of chirality: resolution of precursor, stereoselective reactionAbsolute configuration: (SP,SP,5R,6R)

(SP,SP,5S,6S)-endo-5-exo-6-Di(methylphenylphosphanoyl)bicyclo[2.2.1]hept-2-eneEe 98%, de 90%[α]D20=+15.4 (c 0.72, CHCl3)Source of chirality: resolution of precursor, stereoselective reactionAbsolute configuration: (SP,SP,5S,6S)