Synthesis of the key component for preparation of 6-ketoprostaglandins by a two-component coupling process: Synthesis of 6-keto-prostaglandin E1, ornoprostil and Δ2-trans-6-ketoprostaglandin E1
Starting with commercially available (3S,4R)-3-(methoxymethyloxy)-2-methylidene-4-siloxycyclopentanone 2, useful 6-keto-prostaglandin intermediates 1 have been prepared in good yields by a sequence of reactions which includes treatment with NaBr in the presence of BF3·OEt2, Pd-catalysed coupling of the resulting 2-bromomethyl-4-siloxycyclopent-2-enone 3 with the alkenylborane 4 or 9 and conversion of the alkenyl moiety into an epoxy and then into a keto group. The synthesis of 6-keto-PGE1, ornoprostil and Δ2-trans-6-keto-PGE1 by using 1 is also described.
Nitro-Olefin Trapping Reactions of Enolates In Situ Generated by Conjugate Addition Reaction: Short Syntheses of PGE1, 6-Oxo-PGE1, 6-Oxo-PGF1α, and PGI2
The nitro-olefin trapping of the enolates in situ generated by conjugate addition of organocopper reagents to the chiral oxygenated cyclopentenone synthon, R-4, gives the three-component coupling products in a regiospecific manner.The intermediary nitronate anion 17 is further transformed into the nitro compound or 6-oxo-PGE1 (19) in a single pot.This coupling reaction is applicable to syntheses of naturally occurring prostaglandins such as PGE1, 6-oxo-PGF1α, and PGI2.