The dimesitylboron group in organic synthesis 8. Preparations of 1,3-diols from oxiranes

Alkyldimesitylboranes, yield anions¹, Mes₂B$\text{C}$HR, that on reaction with oxiranes followed by oxidation give 1,3-diols. These anions are thus the operational equivalent of R$\text{C}$HOH. The scope and limitations of the new process are delineated.     

A stereoselective synthesis of 1,2-diols from α-hydroxyaldehydes

The addition of lithium acetylides to (20R)-20-hydroxypregnane-22-carboxaldehydes in the absence and in the presence of BF₃ afforded predominantly 20R,22R- or 20R,22s-diols, respectively, characteristic of ecdysones.     

Silafunctional compounds in organic synthesis. 30. Intramolecular hydrosilation of alkenyl alcohols: A new approach to the regioselective synthesis of 1,2- and 1,3-diols

Intramolecular hydrosilation of allyl and homoallyl alcohols and the subsequent oxidative cleavage of the resultant carbon—silicon bond have provided a new approach to the regio-controlled synthesis of 1,2- and/or 1,3-diols.     

A novel method of synthesis of 1,2-diketones from 1,2-diols using N-bromosuccinimide

A simple and convenient procedure is reported for the synthesis of benzils and aliphatic 1,2-diketones of cyclic and open chain compounds from corresponding hydrobenzoins and 1,2-diols by refluxing with N-bromosuccinimide in carbon tetrachloride in presence or absence of pyridine.     

Heterobimetallic alkyne complexes in organic synthesis: An asymmetric variant of the Pauson-Khand reaction

The use of heterobimetallic alkyne complexes for the synthesis of cyclopentenones is described. The inherent chirality of the complexes has been used to effect high levels of stereocontrol in transformations giving optically enriched organic end products.     

Epoxide hydrolase-catalyzed enantioselective synthesis of chiral 1,2-diols via desymmetrization of meso-epoxides. lzhao@diversa.com

The discovery, from nature, of a diverse set of microbial epoxide hydrolases is reported. The utility of a library of epoxide hydrolases in the synthesis of chiral 1,2-diols via desymmetrization of a wide range of meso-epoxides, including cyclic as well as acyclic alkyl- and aryl-substituted substrates, is demonstrated. The chiral (R,R)-diols were furnished with high ee's and yields. The discovery of the first microbial epoxide hydrolases providing access to complementary (S,S)-diols is also described.     

The reaction of 1,2-dilithiotetrafluorobenzene with group V halides

Although the arsenic containing analogue of triptycene, 5,10-$\text{o}$-benzenoarsanthrene $\text{A}$ (E=As) was isolated some time ago [1] the related derivatives of antimony and bismuth are unknown. We now find that when 1,2-diiodotetrafluorobenzene is treated with methyllithium at -78/dg, to afford the little studied dilithiotetrafluorobenzene [2], and the appropriate metal chloride is added to the resulting solution, perfluorinated analogues of $\text{A}$ (E = As, Sb, or Bi) are obtained in good yield. These are stable volatile solids.

     

A one-step procedure for the monoacylation of symmetrical 1,2-diols

A series of lanthanide (III) salts have been shown to catalyze the monoacylation of symmetrical 1,2-diols by carboxylic acid anhydrides with surprisingly high selectivity.     

Direct catalytic enantio- and diastereoselective aldol reaction using a Zn-Zn-linked-BINOL complex: a practical synthesis of syn-1,2-diols

[reaction: see text] The direct catalytic enantio- and diastereoselective aldol reaction with 2-hydroxy-2'-methoxyacetophenone proceeded smoothly using as little as 1 mol % of a dinuclear zinc catalyst, Zn-Zn-linked-BINOL complex 2, to afford alpha,beta-dihydroxy ketones in a highly syn-selective manner (up to syn/anti 97/3) and in excellent yields (up to 95%) and ees (up to 99%). Efficient transformations of the alpha,beta-dihydroxy ketone into an alpha,beta-dihydroxy ester and an alpha,beta-dihydroxy amide via regioselective rearrangements are also described.     

A mild procedure for the conversion of 1,2-diols to olefins

An improved procedure for the stereospecific synthesis of olefins from 1,2-diols via the corresponding thionocarbonate is described.     

A practical method for synthesis of terminal 1,2-diols in high enantiomeric excess via oxazaborolidine-catalyzed asymmetric reduction

Asymmetric borane reduction of α-hydroxy ketones protected with a tetrahydropyranyl (THP) group catalyzed by Corey's CBS reagent using N-phenylamine–borane complexes as the hydride source provided the corresponding terminal 1,2-diols with a very high enantiomeric excess.     

Lewis acid catalyzed ring opening reaction of cyclobutane-1,2-diols having 1-alkoxyalkyl substituents. Selective synthesis of α,α-disubstituted β-hydroxycyclopentanones

On treating with stannic chloride, silyl ethers of cyclobutane-1,2-diols having 1-alkoxyalkyl substituents at 1-position undergo a facile ring opening reaction to afford the corresponding β-hydroxycyclopentanones or 1,4-diketones in good yield.     

The direct catalytic asymmetric alpha-aminooxylation reaction: development of stereoselective routes to 1,2-diols and 1,2-amino alcohols and density functional calculations

Proline-catalyzed direct asymmetric alpha-aminooxylation of ketones and aldehydes is described. The proline-catalyzed reactions between unmodified ketones or aldehydes and nitrosobenzene proceeded with excellent diastereo- and enantioselectivities. In all cases tested, the corresponding products were isolated with >95 % ees. Methyl alkyl ketones were regiospecifically oxidized at the methylene carbon atom to afford enantiomerically pure alpha-aminooxylated ketones. In addition, cyclic ketones could be alpha,alpha'-dioxidized with remarkably high selectivity, furnishing the corresponding diaminooxylated ketones with >99 % ees. The reaction mechanism of the proline-catalyzed direct asymmetric alpha-aminooxylation was investigated, and we performed density functional theory (DFT) calculations in order to investigate the nature of the plausible transition states further. We also screened other organocatalysts for the asymmetric alpha-oxidation reaction and found that several proline derivatives were also able to catalyze the transformation with excellent enantioselectivities. Moreover, stereoselective routes for the synthesis of monoprotected vicinal diols and hydroxyketones were found. In addition, short routes for the direct preparation of enantiomerically pure epoxides and 1,2-amino alcohols are presented. The direct catalytic alpha-oxidation is also a novel route for the stereoselective preparation of beta-adrenoreceptor antagonists.     

A simplified procedure for the stereospecific transformation of 1,2-diols into epoxides

A simple, ‘one-pot’ procedure for the conversion of vicinal diols into epoxides via halohydrin ester intermediates has been developed. This method tolerates a wide range of functionality including acid sensitive functional groups. The transformation proceeds via a, usually highly regioselective, nucleophilic opening of a cyclic acetoxonium intermediate, generated from a cyclic orthoacetate and Me₃SiCl, acetyl bromide or acetyl chloride/NaI to form 1-acetoxy-2-chloride, 1-acetoxy-2-bromide or 1-acetoxy-2-iodide intermediates, respectively. No epimerization occurs, even with benzylic substrates. Subsequent base mediated methanolysis furnishes epoxides in excellent overall yield. Application of this method led to an efficient formal synthesis of the leukotriene antagonist SKF 104353, commencing with the highly enantioselective cis-dihydroxylation of methyl 3-[2-(8-phenyloctyl)phenyl]propenoate.     

Stereoselective synthesis of anti-1,4-diols by a BH3.THF-mediated rearrangement of 1,2-disubstituted cyclobutenes

A new stereoselective rearrangement of cyclobutylboranes, obtained by the hydroboration of 1,2-disubstituted cyclobutenes, provides anti-1,4-diols with good-to-excellent diastereoselectivity. The mechanism of the rearrangement is discussed based on theoretical calculations.     

Unexpected remarkable stability of primary ozonides derived from alkenyl stannanes. One-pot synthesis of 1,2-diols from alkynes

Primary ozonides derived from alkenyl stannanes display an unusual stability and can be transformed into 1,2-diols by treatment with dimethyl sulfide and borane-methyl sulfide complex. This observation has been incorporated into the development of a novel one-pot strategy for the conversion of alkynes into 1,2-diols.