Olefins acyclic trisubstituted

Similarly poor diastereoselectivity was also observed in 1-substituted cyclohexenes 14 and acyclic trisubstituted olefin substrates 17 (Tables 1.2 and 1.3). Despite the excellent chemoselectivity and enantioselectivity that Rh2(S-DOSP)4 carbenoids generally achieved, the diastereoselectivity was unsatisfactory. It is worth mentioning that the reaction occurs preferentially at the sterically less hindered allylic site. 

Asymmetric hydroboration.1 This borane effects enantioselective hydroboration of rr. v-trisubstituted acyclic and cyclic olefins to provide, after oxidation, (R)-alcohols with optical purities of 60 78% ee. The steric requirements of 1 are less than those of diisopinocampheylborane(l, 262-263 4, 161), but greater than those of isopinocam-phcylborane (8,267). 

Corey and Yamamoto 233) used the P-oxido synthesis 2341 of trisubstituted olefins for the preparation of the acyclic sesquiterpene famesol 433. In this preparation the isoheptenylphosphonium salt 430 is converted into the hydroxyfamesol derivative 432 by reaction with the tetrahydropyranyl ether — protected hydroxy aldehyde 431 and formaldehyde 205. 432 is converted into famesol 433 via several steps. Other reactions of432 likewise proceeding via several steps lead to 434 which is a positional isomer of a C17-juvenile hormone 233) (Scheme 75). 

Perhaps the most basic form of the olefin metathesis reaction is the cross metathesis (CM) of acyclic olefins to yield new acyclic olefins (Fig. 4.11). The ratio of CM products may be controlled by steric and electronic factors to provide one product preferentially, rather than a statistical mixture, which is key to the synthetic utility of this reaction. For example, various functionalized olefins, dimers with bioactive substituents, and trisubstituted olefins have all been made by CM [33], and one of the industrial applications is the synthesis of insect pheromones [34]. 

The present procedure was successfully applied to Oxidation-Reduction Hydration of various olefins. As shown in Table 3, both of acyclic and cyclic olefins were hydrated in high yields based on cobalt(II) catalyst. Exo- and trisubstituted olefins were converted into the corresponding tertiary alcohols in more than 10000% yield based on the catalyst (Entries 2 and 4 in Table 3). Also, olefinic compounds having functional groups such as ester, acetal and amide groups were hydrated into the corresponding alcohols in high yields without any decomposition. 

Hydroboration of trisubstituted olefin is known to give a single product. An alternative to utilize acyclic A-strain effect was demonstrated for high selectivity as shown in Fig. 3, where polar glycol would stay over the sp face so that the... 

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