Preparation of (Z)-Alk-2-ene-1,5-diols by the Titanocene(II)-Promoted Cyclization of Thioacetals Possessing a Terminal Carbon−Carbon Double Bond

Abstract

Titanocene(II)-promoted ring-closing metathesis of the titanium carbene complexes prepared from [2,2-bis(phenylthio)ethyl](but-3-enyloxy)dimethylsilanes or dimethyl(prop-2-enyl)silyl ethers of 3,3-bis(phenythio)propanols gave seven- [a] 155 membered cyclic unsaturated silyl ethers. Oxidative cleavage of a silicon−carbon bond of the cyclic silyl ethers resulted in olefinic diols, with high Z stereoselectivity. silyl ethers of 3,3-bis(phenythio)propanols 5 (Route B). For the preparation of trisubstituted olefins, these two types of cyclization are complementary to each other (Scheme 1).

Novel Synthesis of Trisubstituted Olefins for the Preparation of the C16–C30 Fragment of Dolabelide C

“…When the two-step protocol for tether cleavage was performed on compounds 16, the desired homoallylic alcohols 18 were obtained as 1:1 inseparable mixtures with the corresponding isomerized products. Fortunately, Tamao−Kumada oxidation 14 of the cyclic silyl ethers 16aa, 16ac, and 16ba furnished diols 17aa, 17ac, and 17ba in good yields. Subsequent selective transformation of the primary alcohols into the corresponding bromides and reduction of these bromides (without intermediate purification) with Superhydride gave the desired homoallylic alcohols 18aa, 18ac, and 18ba.…”

Endo-Selective Pd-Catalyzed Silyl Methyl Heck Reaction

“…Its subsequent intramolecular Hosomi–Sakurai reaction with 1,1-dimethoxycyclohexane generated spiro benzofuran 12 in excellent yield (Scheme , a) . Alternatively, 2a can be smoothly oxidized into ( Z )-allylic alcohol 10 in good yield, which highlights employment of halomethylsilanes as a tool for a formal ( Z )-hydroxymethylation of alkenols . Next, we applied this methodology to a cascade process, where a silyl methyl Heck reaction of dienol 1p produced tricyclic compound 2p in excellent yield (Scheme , b).…”

3 Transition metals in organic synthesis : Part (ii) Stoichiometric applications

“…It should be noted for the former that a modified procedure is required. 21 Takeda has also reported the Cp Miscellaneous. The pinacol coupling of aldehydes is a widely studied reaction with broad applications.…”

“…Di-and tri-substituted alkenes (22) are obtained in high yields from sulfones (19) and ketones (20) by modification of the Julià-Lythgoe olefination reaction, Scheme 5. 6 The reaction involves in situ capture of intermediary β-alkoxysulfones by benzoyl or trimethylsilyl chloride to give the β-benzoyloxy/ β-trimethylsilyloxy sulfones (21). A smooth SmI 2 reductive elimination process affords the alkenes with E/Z ratios typically in the range of 2:1.…”