Preparation of silyl-protected γ-hydroxylated α,β-unsaturated acetylenic ketones and their reactions with some nucleophiles

ABSTRACT

A number of 5-siloxylated 1,1-diethoxy-3-alkyn-2-ones were prepared from the corresponding ketals. The t-butyldiphenylsiloxy derivatives were stable, whereas the trimethylsilyl analogs were unstable. The former compounds were reacted with diethylamine, lithium dimethylcuprate, and 1,3-propanedithiol and gave Michael adducts in good to very good yields. The amine and cuprate gave the conjugated alkenones, the former in a stereospecific manner (Z), the latter stereospecifically (E) in one case but otherwise stereoselectively with an E preponderance. With the dithiol bisaddition occurred, and the corresponding 1,3-dithiane was obtained in excellent yield. Attempts to make 1,3-dithianes from 1,3-propanedithiol and 1,1-diethoxy-4-diethylaminoalk-3-en-2-ones failed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Conjugate addition
• conjugated acetylenic ketones
• dimethylcopper lithium
• 1,3-dithianes
• propargylic alcohols
• silyl protection

Acknowledgment

Thanks are also due to Bjarte Holmelid at the University of Bergen for skillful recording and valuable discussions of mass spectra.