3‐Triethylsilyloxypentadienyllithium, a Versatile 1,3‐Diene‐ or Vinyl Ketone‐Building Block

Abstract

Dedicated to Prof. Vludirnir Prelog on the occasion of his 75th birthday (24. VIII. 81) SummaryDeprotonation of the 3-trialkylsilyloxy-1,4-diene 3a and subsequent electrophilic substitution of the non-isolated 3-trialkylsilyloxypentadienyllithium 4 gives the a-and y-products 8 and/or 6 in good yields. Whereas alkylation of 4 proceeds with variable regioselectivity (Table 1) aldehydes and ketones attack preferentially the y-position of 4 ( Table 2). The desired y-products 6 may be directly subjected to interand intramolecular [4 + 21-additions as demonstrated by the reactions 5a (= 6d) ---+ 7 and 6h + 19 (Schemes 4 and 12). Alternatively, smooth fluoride-promoted silylether-cleavage 6 -+ 11 (Scheme 8) provides a convenient approach to substituted vinyl ketones such as to the natural product l l f ( Table 3). The stereoselective conversion 6k -+ 23 (Scheme 13) implies an endo-selective intramolecular Diels-Alder addition (26 -, 23) and exemplifies the use of 4 as an equivalent of the hypothetical anion IV.

Regiocontrolled One-Step Synthesis of 3,3′-Disubstituted 2,2′-Bipyridine Ligands by Cobalt(I)-Catalyzed Cyclotrimerization

“…With a view to facilitating subsequent manipulation of the substituent, and to evaluate the influence of a bulky group separated from the diyne unit by −CH 2 O−, the triethylsilyl ether 2 e 26 was also employed. Not unexpectedly, with 2 e the bulk of the triethylsilyl group did not impede the second cyclization, and there was in fact a slight improvement in the ratio of the 2,2′‐product ( 6 e , 36 % yield) to the 2,3′‐product ( 7 e , 9 % yield); see Table 1.…”

Cobalt-Mediated η5-Pentadienyl/Alkyne [5 + 2] Cycloaddition. Synthesis and Characterization of Unbridged η2,η3-Coordinated Cycloheptadienyl Complexes

“…IR spectra were recorded on either a Nicolet Magna 750 FTIR spectrometer or a Nic-Plan FTIR microscope. 1 H NMR and 13 C NMR spectra were recorded on either a Varian Unity-Inova 300 ( 1 H, 300 MHz), Varian Unity-Inova 400 ( 1 H, 400 MHz; 13 C, 100 MHz), Varian Mercury 400 ( 1 H, 400 MHz; 13 C, 100 MHz), Varian Unity-Inova 500 ( 1 H, 500 MHz; 13 C, 125 MHz), Varian DirectDrive 500 ( 1 H, 500 MHz; 13 C, 125 MHz), or a Varian Unity-Inova 600 ( 1 H, 600 MHz) spectrometer. High-resolution mass spectra were obtained on an Applied Biosystems Mariner Biospectrometry Workstation (electrospray ionization) and elemental analyses were performed by the University of Alberta Microanalysis Laboratories.…”

Synthesis of a 11C‐labelled taxane derivative by [1‐11C]acetylation

“…To avoid the known epimerization of the hydroxy group in position 7 and to stabilize the ester group in position 13 the 2 0 and 7 hydroxy groups of 2 were selectively protected as triethylsilyl ethers. 5 This protection procedure was carried out using triethylsilyl chloride and imidazole in DMF to afford compound 3 in 59% yield. Precursor 3 contains the sterically hindered hydroxy group in position 10.…”