Cis- diol

It is essential to apply both tests, since some symmetrically substituted ethylenic compounds (e.g., ilbene C4H5CH=CHCjHj) react slowly under tbe conditions of the bromine test. With dilute permanganate solution the double bond is readily attacked, probably through the intermediate formation of a cis diol ... 

Acetonides are the most suitable base-stable protecting group for 16,17-cis-diols. They can be readily prepared from 16,17-disecondary alcohols with either the a- or j5-configurations. ... 

Tetramethoxybutane, TMOF, MeOH, CSA, 54-91% yield, trans-Diols are protected in preference to c/5-diols, in contrast to acetonide formation, which prefers protection of cis-diols." ... 

Phenylboronic acid in particular has proved invaluable, since its complexes with cis-diols and -polyols have formed the basis... 

Diols can be prepared either by direct hydroxylation of an alkene with 0s04 followed by reduction with NaHSOj or by acid-catalyzed hydrolysis of an epoxide (Section 7.8). The 0s04 reaction occurs with syn stereochemistry to give a cis diol, and epoxide opening occurs with anti stereochemistry to give a trans diol. 

One of the first uses of the allylic sulfoxide-sulfenate interconversion was made by Jones and coworkers64, who reported exclusive suprafacial rearrangement of the allyl group in the steroidal sulfoxide 17 shown in equation 13. Two other examples are shown in equations 1465 and 1566. Evans and coworkers have demonstrated the utility of the suprafacial allylic sulfoxide-sulfenate rearrangement in a new synthesis of the tetracyclic alcohol 24 (equation 16)67, as well as in a synthesis of prostaglandin intermediates as shown in equation 1768. The stereospecific rearrangement of the unstable sulfenate intermediate obtained from the cis diol 25 indicates the suprafacial nature of this process. 

Metabolic pathways containing dioxygenases in wild-type strains are usually related to detoxification processes upon conversion of aromatic xenobiotics to phenols and catechols, which are more readily excreted. Within such pathways, the intermediate chiral cis-diol is rearomatized by a dihydrodiol-dehydrogenase. While this mild route to catechols is also exploited synthetically [221], the chirality is lost. In the context of asymmetric synthesis, such further biotransformations have to be prevented, which was initially realized by using mutant strains deficient in enzymes responsible for the rearomatization. Today, several dioxygenases with complementary substrate profiles are available, as outlined in Table 9.6. Considering the delicate architecture of these enzyme complexes, recombinant whole-cell-mediated biotransformations are the only option for such conversions. E. coli is preferably used as host and fermentation protocols have been optimized [222,223]. 

S-aryl), concomitant sulfoxidation can be observed and the diastereoselectivity relative to the cis-diol depends on the nature of the sulfur substituents [239]. 

Usually, the polarity of compounds increases by dihydroxylation to such an extent that re-entry into the active site of dioxygenases is not possible and only single microbial biooxygenation is observed. Ho vever, vhen diols are masked in the form of lipophilic acetonides, a second biooxygenation reaction is possible the diastereoselectivity of both cis-diol systems vas reported to be trans (Scheme 9.30) [240]. 

The site of dihydroxylation in heterocycles depends on the nature of the heteroaromatic system (Scheme 9.31) usually, electron-rich heterocycles like thiophene are readily biooxidized but give conformationally labile products, vhich may undergo concomitant sulfoxidation [241]. Electron deficient systems are not accepted only pyridone derivatives give corresponding cis-diols [242]. Such a differentiated behavior is also observed for benzo-fused compounds biotransformation of benzo[b] thiophene gives dihydroxylation at the heterocyclic core as major product, while quinoline and other electron-poor systems are oxidized at the homoaromatic core, predominantly [243,244]. 

Dioxygenases that are exploited at present do not provide general access to antipodal cis-diols and a combined chemoenzymatic strategy is required. While oxidation of bromobenzene (and other mono- and dihalogenated precursors) with TDO expressing cells gives the corresponding (—)-dihydrodiol in excellent... 

The location of the position of double bonds in alkenes or similar compounds is a difficult process when only very small amounts of sample are available [712,713]. Hass spectrometry is often unsuited for this purpose unless the position of the double bond is fixed by derivatization. Oxidation of the double bond to either an ozonide or cis-diol, or formation of a methoxy or epoxide derivative, can be carried out on micrograms to nanograms of sample [713-716]. Single peaks can be trapped in a cooled section of a capillary tube and derivatized within the trap for reinjection. Ozonolysis is simple to carry out and occurs sufficiently rapidly that reaction temperatures of -70 C are common [436,705,707,713-717]. Several micro-ozonolysis. apparatuses are commercially available or can be readily assembled in the laboratory using standard equipment and a Tesla coil (vacuum tester) to generate the ozone. Reaction yields of ozonolysis products are typically 70 to 95t, although structures such as... 

Ketoaldehydes and 1,4-diketones are reduced to cA-cyclopentanediols 258 1,5-Diketo compounds can be cyclized to cyclopentanediols, again with a preference for cis-diols.259 These reactions are believed to occur through successive one-electron transfer, radical cyclization, and a second electron transfer with Sm2+ ether serving as a tether and Lewis acid, as well as being the reductant. 

Dehydration of cortisone (198) affords the diene 199. This is then converted to ketal 200. The selectivity is due to hindrance about both the 11- and 20-carbonyl groups. The shift of the double bond to the 5,6-position is characteristic of that particular enone. Treatment of protected diene 200 with osmium tetroxide results in selective oxidation of the conjugated double bond at C-16,17 to afford the cis-diol (201). Reduction of the ketone at C-ll (202) followed by hydrolysis of the ketal function gives the intermediate 203. Selenium dioxide has been... 

Another cis-diol (XV) derived from BP was obtained by the action of osmium tetroxide on 4,5-dihydroxybenzo[a]pyrene (86). The hydroxyl group at C5a is axial and that at C6 is equatorial, illustrating the relative rigidity of the BP ring system and the flexibility at C6 of the ring bearing the diol groups. 

Seela, F., and Waldeck, S. (1975) Agarose linked adenosine and guanosine-5 -monophosphate a new general method for the coupling of ribonucleotides to polymers through their cis-diols. Nucleic Acids Res. 2, 2343-2349. 

Selective reaction at the ci.s-2,3-diol grouping of unprotected D-ribonucleosides has occasionally been observed. Treatment of D-ribonucleosides with tris(tetramethylammonium) trimetaphosphate in M sodium hydroxide for 4 days at room temperature led to a mixture of nucleoside 2 - and 3 -phosphates in yields of >70% no 5 -phosphate was detected.213 Reaction of ethyl (trichloromethyl)phos-phonate with nucleosides in N,N-dimethylformamide containing triethylamine, followed by basic hydrolysis of the reaction product, yielded 2 (3 )-phosphates in variable yields.214 The participation of the cis-diol grouping in the reaction was suggested by the failure of thymidine or 2, 3 -0-isopropylideneuridine to undergo reaction. 

Ring A diosterols.3 The ring A diosterols (3 and 4) of triterpenes can be prepared from the A2-alkene (1) by osmylation to form the two possible cis-diols (2), which on Swern oxidation give the a-diketone (3). The same diketone is also obtained by Swern oxidation of the 2(3,3a-diol, the product of peracid oxidation followed by acid cleavage. The diketone 3 rearranges to the more stable diosphenol (4) in the presence of base. 

The optical spectra of cis-diols 223 and 224 showed strong absorptions at longer wavelengths with Q bands at 730 and 702 nm, respectively. This trend of longer wavelengths upon dihydroxylation was also observed for seco-pz 225 with a strong absorption at 768 nm, a red shift of 66 nm when compared to pz 223. 

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