Stereoselectivity olefin cross-metathesis

Recently, our group has reported the feasibility of the Sn2 reaction for the stereoselective synthesis of substituted O-heterocycles (Scheme 3.2) [15]. We applied the intramolecular 8 2 reaction in conjunction with an olefin cross-metathesis (CM) reaction (tandem CM/Sn2 reaction) to the stereoselective synthesis of the 2,3-frani-2,5-fra j-tetrahydrofuran of subglutinol B (3.15). 

Via stereoselective ethenolysis of 1,5-cyclooctadiene (COD), Bykov et al. [25] prepared l,d5-5,9-decatriene, a precursor for the synthesis of many ds-isomeric insect sex pheromone compounds. In the presence of the MoCl5/Si02/Me4Sn catalyst system, at 20 °C and an ethene pressure of 25 bar, a 80 % conversion of COD was obtained with a selectivity of 68.4% for l,ds-5,9-decatriene. From this triene, many long-chain (CiQ-Cig) unsaturated acetates, alcohols and aldehydes can be obtained with the required biologically active cis conformation. Cross-metathesis of cyclooctene with a-olefins in the presence of the same catalyst gave... 

The efficient and stereoselective cross-metathesis of vinylsilanes canying electron-withdraAving substituents with various olefins has likewise been described (Eq. 9) [15]. 

Similarly, the cross-metathesis of divinyl-substituted disiloxanes with olefins proceeds in the presence of 5-10 mol % of catalyst I, II, or III in boiling CH2CI2 proceeded stereoselectively producing a mixture of monosubstituted and disubstituted vinylsilanes and ethene and a products of competitive olefin homo-metathesis (Eq. 12). Under the optimum conditions the products were obtained with moderate to high yields. Selected results are summarized in Table 2. 

In summary, alkene cross metathesis has been successfully applied to numerous total syntheses of complex natural products. In most cases, this reaction can provide high yield, and good regio-, chemo-, and F-stereoselectivities. More importantly, the outcome of selective alkene cross metathesis can be predicted based on the propensity of different olefin for dimerization, making it a reliable transformation for design and implementation of complex natural product synthesis. 

Another strong attribute of the biq chc phosphate 26 is the abiHty to mediate cross-metathesis (CM) with various type I and II olefins [23] as shown in Scheme 4.12 [4bj. Studies performed with R,R,Ps)-26 (synthesized from (J ,J )-l,6-diene-3,5-dioI) provided stereoselective formation of the h-isomer in the presence of the catalyst [Ruj-III. 

Catalytic crossed olefin metathesis can also be used to stereoselectively mono-or bifunctionalise polyolefin dendrimers [6]. Grubbs et al. were already able to... 

The stereoselective synthesis of olefins has been one of the major topics in the arena of organic synthesis for many decades. The methods for olefin synthesis have evolved from classic elimination reactions to more modem methods such as the Wittig reaction and its variants, cross-coupling reactions and olefin metathesis. Numerous reviews are available on these topics. The purpose of this special volume is to cover the most recent advances in this ever-growing field, with a focus oti stereocontrol in C=C double formation. 

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