Phosphoramidite, Mitsunobu reaction

Use of the phosphoramidite ligand (-)-199 proved to be crucial for the enantioselective rhodium-catalyzed crossed [2 + 2 + 2] cycloaddition of alkenyl isocyanate 197 with phenylacetylene 198, which provided the vinylogous amide 200 in 62% yield (98% ee). Thereafter, cycloaddition product 200 underwent a diastereoselective hydrogenation followed by a Mitsunobu reaction to complete the total synthesis of (+)-lasubine II (201). 

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