Cis-l,2-diols

In the hydroboration/oxidation reaction of 2-cyclohexen-l-ol derivatives the regio- as well as the stereoselectivities can be steered in either of two directions by use of different reagents and reaction conditions. Dialkylboranes, e.g., 9-BBN, give mainly tn rs-l,2-diols, whereas with 1,3,2-benzodioxaborole ( catecholborane") in the presence of the rhodium hydrogenation catalyst Rh(PPh3)jCl the trans-1,3-diols become predominant. The cis- 1,2-diols are usually only formed in trace amounts, but the cis-l,3-diols are always produced as byproducts in 10 — 20% yield (D.A. Evans, 1988). 

Reaction of RCHO with 1,3-diene monoepoxides.4 The monoepoxides of butadiene or of isoprene after treatment with CrCl2 and 1A1 (2 l) react with aldehydes to form cis-l,3-diols with a quaternary center at C2. 

Acetal and ketal formation has been widely used in carbohydrate chemistry [8—13], not only for structural and analytical purposes, but also for chromatography [11] and mass spectrometry [14-16]. The formation of ring systems is largely dependent on the availability of ds-1,2- and cis-l,3-diol groupings, and the formation of bi- and tricyclic ring systems is possible where more than one such diol grouping is present. 

Ito, M. Matsuumi, M. Murugesh, M. G. Kobayashi, Y. Scope and Eimitation of Organocuprates, and Copper or Nickel Catalyst-Modified Grignard Reagents for Installation of an Alkyl Group onto cis-4-Cyclopentene-l,3-diol Monoacetate. J. Org. Chem. 2001, 66, 5881-5889. 

The intramolecular oxidative carbonylation has wide synthetic application. The 7-lactone 247 is prepared by intramolecular oxycarbonylation of the alke-nediol 244 with a stoichiometric amount of Pd(0Ac)2 under atmospheric pressure s]. The intermediate 245 is formed by oxypalladation, and subsequent CO insertion gives the acylpalladium 246. The oxycarbonylation of alkenols and alkanediols can be carried out with a catalytic amount of PdCl2 and a stoichiometric amount of CuCl2, and has been applied to the synthesis of frenolicin[224] and frendicin B (249) from 248(225]. The carbonylation of the 4-penten-l,3-diol 250, catalyzed by PdCl2 and CuCl2, afforded in the cis-3-hydroxytetrahydrofuran-2-acetic acid lactone 251(226]. The cyclic acetal 253 is prepared from the dienone 252 in the presence of trimethyl orthoformate as an accepter of water formed by the oxidative reaction[227]. 

Synthesis of 1,3-butadienyl ethers is different from that employed when R is a simple alkyl group. David and coworkers350 351 elaborated two approaches to dienyl ethers. In the first method, a sugar derivative (650) having an isolated hydroxyl group3510 reacts under basic catalysis with 2,7-dimethyl-3,5-octadiyne-2,7-diol (651) to yield two en-ynyl ethers (652 and 653). Partial hydrogenation of 652 and 653 gives trims- and cis-l,3-butadienyl ethers (654 and 655) see Scheme 12. 

A highly diastereoselective alkenylation of cis-4-cyclopentene-l, 3-diols has been achieved with O-protected (Z)-1-iodo-l-octen-3-ols and palladium catalyst (S. Torii, 1989). The (E)-isomers yielded 1 1 mixtures of diastereomeric products. The (Z)-alkenylpalladium intermediate is thought to undergo syn-addition to the less crowded face of the prochiral cyclopentene followed by syn-elimination of a hydropalladium intermediate. 

Naphthalene oxides. The Diels-Alder reaction of 1,4-diacetoxybutadiene (1) with benzyne (generated from o-benzenediazonium carboxylate, 1, 46) gives the diacetate of l,4-dihydronaphthalene-cis-l,4-diol (2) in 53% yield. The product is converted into 3 by reaction with hydrogen peroxide and catalytic amounts of osmium tetroxide. The monotosylate of 3 is converted into 4 by treatment with base. This epoxy diol has the stereochemistry found in the carcinogenic epoxy diols formed as metabolites of aromatic hydrocarbons. The dimesylate of 3 is converted into the syft-diepoxide 5. 

On the other hand, higher 1,2-asymmetric induction is observed for the cyclization of 5-aIkenols which bear an oxygenated function at C-4. Thus, treatment of 5-hexen-1,4-dioI (3) with phenyl-selenyl triflate in dichloromcthanc at —78 °C gives the corresponding tetrahydro-2/f-pyran 4 in 52% yield as a 91 9 (cis/trans) mixture. The preferential 2,3-cis relationship can be explained by analogy with the halocyclization of 4-pentene-l,3-diols (see Section 4.6.2.1.1.3.)19. 

Asymmetric Intramolecular Hydrosilation. Intramolecular hydrosilation of allylic alcohols followed by oxidation is a convenient method for the stereoselective preparation of 1,3-diols. An enantioselective version is achieved by use of diene-free BINAP-Rh+ (eq 6). Both silyl ethers derived from cinnamyl alcohol and its cis isomer give (iJ)-l-phenylpropane-l,3-diol in high ee regardless of alkene geometry. 

Oxidation of cyclohexanol by H2O2 in the presence of Fe(C104)2 and perchloric acid in acetonitrile was found to give cyclohexanone and the six possible cyclohexanediols in which cis-l,3-cyclohexanediol represented 72% of the total amount of diols produced. This unusual... 

Ketones react with alcohols to yield products called acetals. Why does the all-cis isomer of 4-terf-butylcyclohexane-l,3-diol react readily with acetone and an acid catalyst to form an acetal, but other stereoisomers do not react In formulating your answer, draw the more stable chair conformations of all four stereoisomers and the product acetal. Use molecular models for help. (Sec Section 19.11.)... 

Diols Both cis- and tran5-l,3-diols form cyclic acetals with aldehydes in the presence of an acid catalyst to furnish the corresponding benzylidene and ethylidene derivatives, respectively. 

Compounds bearing ci.r-l,2-diols and cis- and rrans-l,3-diols can be protected as cyclic acetals and ke-tals or cyclic orthoesters. As has been shown for ethers, these blocking groups are stable to bases but are... 

DL-erythro(threo)-2-amino-4-trans(cis)-decene-l,3-diol 38... 

---