Bisallylic alcohols

Double Sharpless epoxidation was also applied to the synthesis of a key intermediate 10 to the meso-compound 11 that is related to teurilene, abioactive polycyclic triterpene isolated from red alga Laurencia obtusa,4 The reaction of ( , )-Bisallylic alcohol 9 gave the bisglycidic alcohol 10 with 80% de and 89% ee for each epoxidation (Scheme 6AA.4). 

Similarly, the selective epoxidation of the bisallylic alcohol (XII) to the bis-epoxyalcohol (XIII), with (-Bu02 H-VO(acac)2, is the crucial step in a synthesis of juvenile hormone from farnesol467 ... 

AE of the meso-bisallylic alcohol 17 has also been examined [54]. In this class of substrate, the first epoxidation occurs smoothly in a highly enantiotopic selective manner to give the mono-epoxide 18 preferentially but the second epoxidation of 18 is slow. Therefore, the mono-epoxide 18 can be obtained as a major product in a highly enantiopure form (98% ee) together with a small amount of the diepoxide. 

The absolute stereochemistry of abscisic acid (57) has at last been established. Owing to the unusual bisallylic alcohol function, the previous assignment based on Mills rule was incorrect and this has now been reversed so that it is consistent with violaxanthin (54). Oritani et al. showed that ( —)-a-ionone (56) was converted in to (— )-abscisic acid with retention of configuration (their enantiomers... 

The first examples of intramolecular AHRs were reported by Shibasaki et al. [123] and Overman et al. [124] in 1989. The Shibasaki group carried out cycliza-tion of achiral alkenyl iodide or triflate 300 to give the chiral tetrahydronaph-thalene system 301 by differentiation of enantiotopic C=C double bonds using (i )-BINAP without using a silver salt [123]. Subsequently, the reaction has been improved [125]. The chiral hexahydronaphthalene system 304 with 86% ee was obtained by AHR of the bisallylic alcohol 302 via syn j6-H elimination from the intermediate 303, and 304 was converted to the key intermediate 305 in the synthesis of vemolepin (306). Use of a mixed solvent of 1,2-dichloroethane and r-BuOH is important [126]. 

In addition, the bisallylation of the two secondary amides of compound 91, followed by treatment with an appropriate ruthenium catalyst, allowed a tandem ringopening metathesis/ring-closing metathesis to give, after alcohol deprotection, the quite complex structure 92 [82]. 

Self-irnmolative chirality transfer for rr-sLabilized [2,3] Wittig systems derived from nonracemic secondary alcohols follows a stereochemical course consistent with rearrangement through the conformation (vide supra). For bisallylic ethers 46, the fidelity of chiral transmission is larger than 90%34. 

The allyl-transfer method was extended to functionalised disilane 21.42," which represents a potentially bisallylic system with an orthogonal reactivity of the two moieties (Scheme 21.5). Indeed, allylation of a variety of aromatic and a,p-unsaturated aldehydes 21.4 with the latter reagent, catalysed by METHOX (21.26) and QUINOX (21.27), afforded the expected homoallylic alcohol 21.44 in high stereocontrol (<97% enantiomeric excess and >99 1 dr). However, the reaction takes 7-10 days, which is less than practical. 

Trimethylsilyl iodide is known to convert alcohols into iodides but is very sensitive to hydrolysis, so some new mild methods have been developed for the in situ generation of this reagent under neutral conditions. The reaction of allyltrimethylsilane and iodine does generate MeaSil, but the allyl iodide byproduct is not compatible with the presence of nucleophilic groups. A better solution is to use the bisallylic silane (58) and iodine (Scheme 38), where the other product is benzene. Trimethylsilyl bromide, although much less electrophilic... 

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