Bicyclic triols

The reactions provided trioyclolactones 52a - 56a in good yields and endo/exo selectivity except entry 5, in which the formation of the exo-isomer prevailed. The resultant cycloadducts can be readily manipulated into bicyclic triols as exemplified with 54a. Reductive removal of tertiary alkyl bromide (vide infra) and reductive cleavage of the lactone afforded 58 in good overall yield (Scheme 16). 

The use of 1,2- and 1,3-diols in the transesterification reaction provides a means of providing monocyclic ortho esters [49-54]. Cycloalkanediols or acyclic triols result in bicyclic [55] and polycyclic ortho esters [56, 57] (Eqs. 22, 23). 

Reduction of the olefinic bond in 12 and Swem oxidation of the free carbinol function provided ketone 53, onto which installation of the methyl group was performed by reaction with methylmagnesium chloride in THF. After protection of the resulting tertiary alcohol as a TBS-ether, fully protected triol 54 was obtained with a useful 80% diastereomeric excess. Acetonide deblocking and oxidative fission of the diol formed led to aldehyde 55, ready for the planned cyclization step. Exposure of aldehyde 55 to TBSOTTDIPEA reagent system smoothly resulted in formation of the desired bicyclic adducts 56 and 57 which were isolated in a 82% combined yield (60 40 ratio). 

When BuSi(0SiMe20H)3 is heated, poly-condensation is immediately started, forming many different products. In order to synthesize low-molecular condensates, we have reacted BuSi(OSlMe2Cl)3 with one equivalent of the triol BuSi(0H)3 using triethylamine as HCl captor (compare also Eq. 2) the cage like BuSi(0SiMe20)3Si Bu is formed in 60% yield. In Fig. 3 the result of an X-ray structure analysis is depicted. Bicyclic molecules with the same skeleton of atoms but with different substituents are known [20,21]. 

Chemical and spectroscopic evidence has been cited in support of the structure and absolute configuration of cybullol (383), a metabolite of Cyanthus bulleri Brodie. It has been suggestedthat the trisnor-sesquiterpenoid structure of cybullol is produced in nature by elimination of an isopropyl group from a eudesmane precursor, and the structural elucidation of a bicyclic sesquiterpenoid triol which co-occurs with cybullol could eventually provide indirect support for this proposal. 

Bicyclic Carotenoids. Re-investigation of the carotenoids of Anacystis nidulans has confirmed the presence of /3,)8-carotene-2,3,3 -triol (6), and the previously unknown )8,j8-carotene -2,3,2, 3 -tetrol (7) was also isolated. These compounds are considered to be identical with caloxanthin and nostoxanthin, for which allenic structures have previously been suggested. The main carotenoid of Coccolithus... 

Abstraction a to an oxygen atom. Formation of a bicyclic system starting from a free alcohol is depicted in Scheme 40 (Eq. 40.1) [136]. Malacria has recently reported the preparation of enantiomerically pure 1,2,3-triols via an unusual 1,4-hydrogen atom abstraction followed by a highly diastereoselective trapping of the resultant alkoxy substituted radical with acrylonitrile (Eq. 40.2) [19]. In this particular case, intramolecular reaction with the alkenyl group (3-cxo-trig or A-endo-ing cyclization) is not feasible therefore, reaction with an external radical trap is favored. 

The monocyclic 1,3,2-dioxaphosphepine oxide (60) can also be synthesized starting from triol (57) by treating with hexaethylphosphorus triamide, followed by oxidation with ozone and chlorination of the resulting bicyclic compound (59) (Scheme 7) <93ZOB69>. 

These salts can react with a variety of nucleophiles including amines (to afford amidines), alcohols (to afford esters), hydrogen sulfide (to afford thioamides), and isotopically labeled water (to afford 0-labeled amides). Iminium triflates are also excellent intermediates for the preparation of assorted heterocycles. Iminium triflates react with azides (to afford tetrazoles), -mercaptoamines (to afford thiazolines), and triols (to afford orthoesters) (eq 58). The reaction of lactams with Tf20 and sodium azide affords tetrazolo-fused bicyclics. ... 

Petuniasterones with side chains bearing functionalities other than orthoesters also occur. The important PS-B and PS-C series (Figure 2) have epoxy groups at the 24,25-position and hydroxy or acyloxy groups at position-22. We have shown (12) that 22-acyloxy epoxides easily rearrange to the bicyclic orthoesters, and also that a 22-hydroxy epoxide yields the isomeric 5-membered cyclic ether as well as a mixture of side chain triols under mild acid treatment. 

Roberts et al. [46] have enzymatically resolved bicyclic lactone 128 using Pseudomonasfluorescens lipase and vinyl acetate. The enantio-pure ester, (-)-151 (>95% ee), obtained by this process is converted in three steps into diol 153 via triol 152 in 50% overall yield without purification of the intermediates... 

Periodate (s. a. under RuO ) Bicyclic acetalohemiacetals from monocyclic 1,2,3-triols... 

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