Alkenyl thioacetals

Scheme 14.17. RCM of titanocene-alkylidenes generated from alkenyl thioacetals.

This RCM has proven to be a useful synthetic method for the construction of a variety of heterocycles. Mono and bicyclic unsaturated ethers and sulfides are obtained from alkenyl thioacetals having an ether or sulfide linkage (Table 14.2) [30],... 

Reactions of Titanium Carbene Complexes with Carbon—Carbon Double Bonds Table 14.1. Preparation of carbocyclic compounds from alkenyl thioacetals. 

Table 14.2. Preparation of cyclic ethers and sulfides from alkenyl thioacetals. ...

An interesting application of the cydization of alkenyl thioacetals is the stereoselective preparation of olefmic diols. Thus, oxidative cleavage of the silicon—carbon bond [32] in the ring-closed metathesis products, i.e. cyclic allylsilanes such as 35 and 36, affords (Z)-alk-2-ene-1,5-diols 37 and 38 (Scheme 14.18) [33],... 

An unusual reductive elimination can ensue from titanacyclobutanes possessing an alkenyl group at the carbon a to the titanium atom. Thus, alkenylcarbene complexes 48, prepared by the desulfurization of (fy-unsaturated thioacetals 49 or l,3-bis(phe-nylthio)propene derivatives 50 with a titanocene(II) reagent, react with terminal olefins to produce alkenylcyclopropanes 51 (Scheme 14.22, Table 14.4) [37]. This facile reductive... 

Equilibrium data are also available for some Ag1 complexes with alkyl-, alkenyl- and phenyl-thioacetic acids. An important conclusion here is that the strength of the Ag—S bond is mainly determined by its o component.34 In addition, the fact that the cis isomer (1) isomerizes to the trans isomer (2) upon moderate heating suggests that there is no strong metal-to-sulfur -interaction.35 Affinity data for other systems have been compiled by Kuehn and Isied.4... 

Alkylidenation with a thioacetal-titanocene(II) system is useful for the conversion of carboxylic acid derivatives into enol ethers, alkenyl sulfides, and enamines. As with other titanium-based reagents, mixtures of stereoisomers are formed in... 

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