Collins Reagent Research Articles

Functionalization of the position 5 of thiopyran fragment of 4-(diethoxyphosphoryl)-4,7-dihydro-5 Н-thiopyrano[3,4-b]furan

Alkaline hydrolysis of ethyl 4-(diethoxyphosphoryl)-4,7-dihydro-5 Н -thiopyrano[3,4- b ]furan-5-carboxylate proceeded selectively at the ester group. The acid obtained formed the corresponding acid chloride when treated with thionyl chloride. The acid chloride was used for acylation of glycine, α- and β-alanine esters. Under the conditions of phase transfer catalysis this acid chloride formed acyl azide which under mild conditions undergoes rearrangement to isocyanate. The latter reacted with primary amines to give ureas, and with the amino acid esters in forms ureidoesters. Reducing of acid chloride with sodium borohydride led to the corresponding alcohol. It was converted to chloride which in the reactions with sodium azide and iodide gives usual substitution products. When treated with potassium thiocyanate it formed thiocyanate. Iodide in the reaction with triethyl phosphite gave the corresponding phosphonate. Oxidation of alcohols with Collins reagent and acetic acid-DMSO system was studied.

ChemInform Abstract: Synthesis of Trifluoromethyl Analogue of L-Fucose and 6-Deoxy-D- altrose.

Trifluoromethylation of the acyclic derivative of D-lyxose, 3, with trifluoromethyltrimethylsilane in the presence of tetrabutylammonium fluoride yielded a mixture of trifluoromethyl adducts, 5a and b, which was converted to 6,6,6-trifluoro-L-fucose 9a and 6-deoxy-6,6,6-trifluoro-D-altrose 9bvia selective oxidation of the primary hydroxy group involving treatment of the trimethylsiloxy derivatives, 7a and b, with Collins reagent.

Reductive and Transition-Metal-Free: Oxidation of Secondary Alcohols by Sodium Hydride

The oxidation of alcohols into their corresponding carbonyl compounds represents a fundamentally important functional group transformation and occupies a prominent position in modern synthetic organic chemistry. Advances on the development of new oxidation reagents and methodologies and their applications in both targetand diversity-oriented synthesis have been regularly surveyed and constituted one of the most extensively and actively investigated areas of current organic synthesis. In this context, a plethora of oxidants, including those small organic molecule-based reagents (such as Dess-Martin periodinane, Swern oxidation, Moffatt oxidation, Corey-Kim oxidation, and SO3/pyridine) and metal-based systems (such as Jones reagent, Collins reagent, pyridinium chlorochromate, pyridinium dichromate, barium permanganate, manganese dioxide, ruthenium tetroxide, silver carbonate, and Oppenauer oxidation), have been identified to be powerful tools promoting conversion of various alcohols into their corresponding aldehyde or ketone products and thus evolved as a most important class of tools in synthetic chemists’ arsenal. A recent conceptually novel approach in alcohol oxidation chemistry, driven by the needs of process environmental compatibility and sustainability, has been exploring aerobic oxidation with highly active transition-metal catalysts (such as Pd, Ru, Fe, Cu, Pt, Au, Ir, Rh, etc.) and dioxygen gas as the terminal oxidant, their heterogeneously immobilized variants, and biomimetic systems. Despite these impressive advances, very few of the known methods are capable of offering truly economic and practical oxidation transformations across a broad spectrum of alcohol substrates. Many of these systems suffered from high reagent cost, air instability, employment of heavy metals or organic oxidants, stringent reaction conditions, operational complexity, functional group incompatibility, or production of wastes in their related processes. Thus, there is a continuing and increasing demand for new reagents that could help address the above-mentioned challenges. We herein report on an exceedingly simple secondary alcohol oxidation protocol that employs the widely available sodium hydride (NaH) as the oxidant.

Zirconium Hydroxide Chromate (Zr4(OH)6(CrO4)5(H2O)2): a Mild and Efficient Reagent for Oxidation of Benzylic Alcohols

Oxidation of primary and secondary alcohols to aldehydes and ketones is one of the most important transformations in organic chemistry both at laboratory and industrial scale. Chromate salts and other chromium (VI) oxides have been widely used as oxidizing agents for a variety of substrates including alcohols. These oxidants are generally used in large excess, but also can be used at catalytic scale in conjunction with secondary oxidants. Recently several chromium(VI) reagents such as: Collins reagent (CrO3. Py), 6

SYNTHESIS OF (6-2H)- AND 6-DEOXY-6-FLUORO-L-GALACTOSE DERIVATIVES11

The selective oxidation of trimethylsilylated D-galactose diethyl dithioacetal using Collins reagent provided the corresponding D-galacto-hexo-dialdo dithioacetal. Successive acid hydrolysis, isopropylidenation, and cleavage of the dithioacetal group gave the 1,2;3,4-di- O-isopropylidene-L-galacto-hexodialdo-1,5-pyranose as a key intermediate for the synthesis of 6-fluoro-and 6-deutero-substituted L-fucose derivatives. 1 Dedicated to Professor Peter Köll on the Occasion of His 60th Birthday.

ChemInform Abstract: Oxidation of Certain 4‐Substituted Phenethyl Alcohols with Collins Reagent: On the Mechanism of a Carbon‐Carbon Bond Cleavage.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxidation of Certain 4-Substituted Phenethyl Alcohols with Collins Reagent: On the Mechanism of a Carbon-Carbon Bond Cleavage

Abstract A mechanism is proposed for a carbon-carbon bond cleavage observed in the oxidation of certain 4-substituted phenethyl alcohols with Collins reagent.

Oxidative rearrangement of sulfur-containing tertiary allylic alcohols: synthesis of 2-cycloalkenones bearing 3-[(phenylthio)methyl] and 3-[2-alkyl-1,3-dithian-2-yl] substituents

Substrate 1-[(phenylthio)methyl]-2-cycloalkenols 3a-d and 1-[2-alkyl-1,3-dithian-2-yl]cyclohexenols 1a-a were prepared by adding [(phenylthio)methyl]lithium and 2-lithio-2-alkyl-1,3-dithianes, respectively, in the 1,2-mode to various 2-cycloalkenones. The ranges of yields for the additions were 86-96% in the (phenylthio)methyl series and 69-88% in the dithiane series. A representative compound from each range of substrate tertiary allylic alcohols was then treated with a series of oxochromium(VI)-amine reagents such as pyridinium chlorochromate (PCC), pyridinium dichromate (PDC), the Collins reagent (CrO 3 .Pyr 2 ), and 2,2'-bipyridinium chlorochromate (BPCC)

Synthesis of trifluoromethyl analogue of L-fucose and 6-deoxy-D-altrose

Trifluoromethylation of the acyclic derivative of D-lyxose, 3, with trifluoromethyltrimethylsilane in the presence of tetrabutylammonium fluoride yielded a mixture of trifluoromethyl adducts, 5a and b, which was converted to 6,6,6-trifluoro-L-fucose 9a and 6-deoxy-6,6,6-trifluoro-D-altrose 9bvia selective oxidation of the primary hydroxy group involving treatment of the trimethylsiloxy derivatives, 7a and b, with Collins reagent.

Syntheses of α, β‐Epoxy Silyl Ketones

AbstractThe synthesis of the α, β‐epoxy‐acylsilanes 1 and 2 starting from the allylic silyl alcohols (E)‐ and (Z)‐3, respectively, by epoxidation with t‐BuOOH/VO(acac)2 followed by oxidation with Collins reagent (CrO3/pyridine) in up to 70% overall yields, is described. The acid‐catalyzed rearrangement of the epoxy‐silyl alcohols 4A + B und 5A + B led to the novel unstable diastereoisomeric α‐silyl‐β‐hydroxy‐aldehydes 9 and 10, respectively. The structure of 10 was established by X‐ray crystal‐structure analysis of the corresponding alcohol 11.

A New Synthesis of an Important Prostaglandin Intermediate by Selective Oxidation of a Trimethylsilylated Primary Alcohol to the Corresponding Aldehyde

The bis(trimethysilyl) ether of the prostaglandin precursor rac-3 was oxidized with high selectivity to the trimethylsilylated Corey aldehyde rac-1f using Collins reagent (chromium(VI) oxide/pyridine) in dichloromethane. This unstable compound was subjected without isolation to a twophase Horner olefination by adding the dimethyl phosphonate 4 and concentrated aqueous sodium hydroxide to the oxidation mixture. Thus, the prostaglandin intermediate rac-5 was obtained in a yield of 35-40% in a convenient one-pot procedure.

The Oxidation of Primary Trimethylsilyl Ethers to Aldehydes – a selective conversion of a primary hydroxy group into an aldehyde group in the presence of a secondary hydroxy group

AbstractSecondary trimethylsilyl ethers (2a–d) are not affected by Collins reagent in dichloromethane at 0°C. Primary trimethylsilyl ethers (4a–e), however, are smoothly oxidized to aldehydes (5a–e) under these conditions. In agreement with these observations trimethylsilylated diols or polyols with primary and secondary trimethylsilyloxy groups (6–9) are oxidized selectively by Collins reagent to trimethylsilyloxy aldehydes (10–13).

Part I. epoxydes diterpeniques : synthese et reactivite d'epoxydes derives d'acides resiniques

Epoxidation of methyl esters of resin acids with the pimarane skeleton with p-nitroperbenzoic acid has permitted the isolation of epoxides of the intracyclic double bond. Allylic diterpenic alcohols were obtained by acid-catalysed isomerisation of diterpene epoxides, and the action of Collins reagent on these allylic alcohols has been studied.

Stereoselective total syntheses of (±)-isoagatholactone and (±)-12α-hydroxyspongia-13(16),14-diene, two marine sponge metabolites

The highly efficient, stereoselective syntheses of (±)-isoagatholactone (1a) and (±)-12α-hydroxyspongia-13(16),14-diene (3e), a fundamental skeleton of spongiadiol (3a) and its related furanoid diterpenes, are described. (±)-Labda-8(20),13-dien-15-oic acid (6), chosen as the starting material, was cyclised to the known tricyclic compound (2b), which after methylation was subjected to photo-oxygenation, yielding the allylic alcohol (7a). Refluxing of the alcohol (7a) with 3.5% sulphuric acid in dioxan afforded the lactone (1b), which after reduction with lithium aluminium hydride led to the diol (2g). Subsequent oxidation of this diol with Collins reagent provided the desired compound (1a). The key precursor for the synthesis of compound (3e) was the allylic alcohol (7a) obtained above. On epoxidation the alcohol (7a) gave the epoxide (13), which by the action with lithium di-isopropylamide led to the α,β-unsaturated γ-lactone (14). Subsequent reduction of this lactone with di-isobutylaluminium hydride afforded the furan (3e).

Collins Oxidation of Methyl (+)-13β-Abiet-8-en-18-oate and Absolute Configuration of Suaveolic Acid

Abstract The oxidation of methyl (+)-13β-abiet-8-en-18-oate with Collins reagent yielded nine oxidation products. Their structures were elucidated on the basis of spectroscopic and chemical data to be methyl (−)-14-hydroxy-7-oxoabieta-8,11,13-trien-18-oate (1% yield), methyl (−)-11,14-dioxoabieta-8,12-dien-18-oate (1%), methyl (+)-11-oxo-13β-abiet-8-en-18-oate (18%), methyl (−)-8α,9α-epoxy-7-oxo-13β-abietan-18-oate (2%), methyl (+)-7-oxoabieta-8,11,13-trien-18-oate (2%), methyl (+)-11,14-dihydroxy-7-oxoabieta-8,11,13-trien-18-oate (2%), methyl (+)-7,11-dioxo-13β-abiet-8-en-18-oate (17%), methyl (+)-14-oxo-13β-abiet-8-en-18-oate (15) (4%), and methyl (+)-7-oxo-13β-abiet-8-en-18-oate (23%) respectively. It is noteworthy that oxygenation occurs not only at the C-7 and C-11 positions but also at the C-14 position. The oxygenated products obtained in this studies could be useful intermediates for the synthesis of the oxidized diterpenoids of abietane skeleton. To exemplify this, 15 was converted to methyl suaveolate and suaveolol. Hydrolysis of the former yielded suaveolic acid, thus confirming its absolute configuration to be 4R, 5R, 10S, 13S, and 14S.

9-epi-leucomycin A5. Synthesis and antimicrobial activity.

9-epi-Leucomycin A5 has been obtained from leucomycin A5 (I) by the following reaction sequence. Leucomycin A5 (I) was treated with Collins reagent (CrO3-pyridine) in the presence of water (13%) to provide 9-dehydroleucomycin A5 (II) in 95% yield. The formyl group was internally protected by the reaction of II with acetic anhydride-K2CO3 to afford 18,2'-di-O-acetyl-9-dehydroleucomycin A5-3,18-hemiacetal (III). Sodium borohydride reaction of II provided a 1 : 1 mixture of natural I and its 9-epimer, 9-epi-leucomycin A5 (IV), which were separated by silica gel chromatography. It was observed that the antimicrobial activities of both enantiomers were virtually identical with some tests strains but that of IV is reduced in comparison with I in some bacteria such as Staphylococcus epidermidis sp-al-1 and Streptococcus pyogenes N. Y. 5.

InSituAllylic Oxidations With Collins Reagent

Abstract Chromium trioxide-pyridine complex (Collins Reagent) oxidizes alcohols to aldehydes and ketones in high yield, and has been particularly effective in oxidizing acid-sensitive alcohols. A great improvement in the utility of the reagent was reported by Ratcliffe and Rodehorst who made the complex in situ in methylene chloride – thus avoiding the problems involved in isolating crystalline complex. The primary problems include keeping the crystalline complex dry; avoiding fires during addition of CrO3 to pyridine; and having to make the complex in a separate step in the first place. Dauben, Lorber, and Fullerton found that the isolated complex is extremely effective in allylic oxidations, i.e. in oxidizing olefins to enones. Shaw and Sherry also were able to oxidize alkynes to acetylenic ketones in low yields with the isolated complex. In unpublished experiments, the in situ Ratcliffe procedure was tried for allylic oxidations – but with poor yields. Shaw and Sherry reported similar problems with the...

Steroids and Steroidases. XVI. An Evaluation of Synthetic Routes to Variously C-17-Substituted Δ5-3-Ketosteroids

Several routes to variously C-17-substituted Δ5-3-ketosteroids have been surveyed. The most convenient method was found to be oxidation of Δ5-3β-alcohol precursors with the Collins reagent, dipyridine chromium trioxide in méthylène chloride. The purities of the desired acid- and base-labile compounds obtained were ≥ 99% in each case.