Prostaglandins and prostaglandin intermediates. Part 26. A novel route to PGF2α using triisopropoxy-hept-1-ynyl-titanium as precursor for the β-side chain
✍ Scribed by Dr. Rainer Mahrwald; Prof. Dr. Hans Schick; Dr. Kasimir K. Pivnitsky; Prof. Dr. Sigfrid Schwarz
- Publisher
- John Wiley and Sons
- Year
- 1990
- Tongue
- English
- Weight
- 777 KB
- Volume
- 332
- Category
- Article
- ISSN
- 1615-4150
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✦ Synopsis
Abstract
The benzoylated Corey aldehyde 1a can be alkynylated with hept‐1‐ynyl‐triisopropoxytitanium in good chemical yield and high diastereoselectivity to the (R)‐alcohol 3c admixed with about 10% of the diastereomeric (S)‐alcohol 2c. Without removal of this admixture the (R)‐alcohol 3c was converted into PGF~2α~, which was easily separated from the accompanying 15‐epi‐PGF~2α~. The main steps of this reaction sequence involve the conversion of a propargylic alcohol into an (E)‐allylic alcohol and the palladium (II)‐catalyzed allylic rearrangement of its acetate. With hept‐1‐ynyllithium the trimethylsilyloxy aldehyde 1b affords the (S)‐alcohol 2c as the predominating product admixed with about 20% of the diastereomeric (R)‐alcohol 3c. Again, without removal of the admixture the (S)‐alcohol 2c was converted into known PGF~2α~ intermediates via the palladium(II)‐catalyzed allylic rearrangement of the corresponding (Z)‐allyl alcohol.