Chemoselective esterification of phenolic acids and alcohols

[formula: see text] The Mitsunobu reaction can distinguish between alcohol and phenol hydroxyls in esterification reactions, providing an expeditious and broadly applicable entry into various phenolics and polyphenolics of biomedical and nutritional relevance.     

Nucleophilic fluorination of amino alcohols and diols using Deoxofluor

Various fluorinated chiral compounds were synthesized using bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor) as a nucleophilic fluorinating reagent. Reactions of Deoxofluor (1) with amino alcohols (2a-d) and diols (2e-g) in methylene chloride at room temperature led to the formation of the corresponding fluoro derivatives (3a-g) in good yields.     

Chemoselective trimethylsilylation of alcohols catalyzed by saccharin sulfonic acid

Abstract  Saccharin sulfonic acid was easily prepared by the reaction of saccharin with neat chlorosulfonic acid at room temperature. This reagent is efficiently able to catalyze the chemoselective trimethylsilylation of alcohols with hexamethyldisilazane in the presence of amines and thiols. Graphical abstract        

Chemoselective S-benzylation of indoline-2-thiones using benzyl alcohols

Indoline-2-thiones were chemoselectively S-benzylated using a variety of benzyl alcohols by boron trifluoride etherate-catalyzed reactions. The aryl substituent effect on the reactivity of the benzyl alcohols toward S-benzylation is also discussed.     

Chemoselective trimethylsilylation of alcohols catalyzed by saccharin sulfonic acid

Abstract  

Saccharin sulfonic acid was easily prepared by the reaction of saccharin with neat chlorosulfonic acid at room temperature. This reagent is efficiently able to catalyze the chemoselective trimethylsilylation of alcohols with hexamethyldisilazane in the presence of amines and thiols.     

Chemoselective nucleophilic fluorination induced by selective solvation of the SN2 transition state

Reaction of the fluoride ion with secondary alkyl halides leads to 90% of elimination reaction and only 10% of nucleophilic substitution in dipolar aprotic solvents. Adding water to the organic phase, the SN2 yield increases in the cost of decreased reactivity. Using ab initio calculations, we have shown that it is possible to increase the reaction rate and the selectivity toward the SN2 process through supramolecular organocatalysis. The catalytic concept is based on selective solvation of the transition state through two hydrogen bonds provided by the 1,4-benzenedimethanol. The two hydrogen bonds between the catalyst and the SN2 transition state favor this pathway while just one strong hydrogen bond between the catalyst and the fluoride ion leads to a lower stabilization of the nucleophile, resulting in a higher reaction rate. Our calculations predict that the substitution product increases to 40% yield because of the selective catalysis provided by the 1,4-benzenedimethanol.     

Synthesis ofβ-fluoro-β-nitro alcohols by direct fluorination

Conclusions The direct fluorination of the sodium salts of 1-nitro-2-propanol, 1-nitromethylcyclohexanol, and 1-phenyl-2-nitroethane yielded-fluoro--nitro alcohols.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1651–1652, July, 1972.     

Chemoselective desulfurization-fluorination/bromination of carbonofluoridothioates for the O-trifluoromethylation and O-bromodifluoromethylation of alcohols

Herein, a method for synthesizing various alkyl trifluoromethyl and alkyl bromodifluoromethyl ethers using carbonofluoridothioates(R–OC(=S)F) as precursors has been described. Carbonofluoridothioates were obtained upon the reaction of an alcohol and S=CF_2 generated via the decomposition of an SCF_3 anion, and then selectively transformed into their corresponding trifluoromethyl and bromodifluoromethyl ethers upon changing the reaction conditions. This transformation has also been extended to the one-pot, two-step conversion of alcohols into alkyl trifluoromethyl ethers. A series of alkyl bromodifluoromethyl ethers has also been synthesized. These compounds open up a new avenue for the synthesis of a wide range of useful fluorinated products. In addition, this method is suitable for the late-stage introduction of trifluoromethyl ethers in complex small molecules.     

Chemoselective oxidation of primary alcohols catalysed by Ce(III)-complex intercalated LDH using molecular oxygen at room temperature

Herein we describe the preparation of an efficient heterogeneous catalyst consisting of an anionic Ce(III)-complex immobilized Zn/Al-layered double hydroxide (LDH) and its use in the catalytic liquid phase oxidation of primary alcohols using molecular O(2) at room temperature. Various primary alcohols could be transformed to their corresponding aldehydes in good to excellent yields using the set of optimal conditions. The heterogeneous catalytic system can also be recovered and reused for several cycles without a significant loss of catalytic activity.     

Chemoselective protection of thiols versus alcohols and phenols. The Tosvinyl group

The conjugate addition of aliphatic and aromatic thiols to ethynyl p-tolyl sulphone (tosylacetylene) has been managed to afford Tosvinyl derivatives chemoselectively (in the presence of oxygen nucleophiles) and stereoselectively (isomers Z) in practically quantitative yields. The conditions of choice are: catalytic amounts of Et₃N (only 0.5-1.0 mol%), a reaction temperature around 0°C and, for the less acidic thiols, CF₃CH₂OH or CH₃CN/CF₃CH₂OH as the solvent. Thus, N-Boc-Cys-OMe has been quantitatively protected as its S-Tosvinyl derivative in the presence of N-Boc-Ser-OMe and N-Boc-Tyr-OMe. This novel protecting group is stable to several basic and acidic conditions; its removal is achieved at rt by treatment with an excess of pyrrolidine or at 0°C with alkanethiolate ions.     

Rearrangements accompanying fluorination of 2-amino alcohols and 1,2-diols with Deoxo-Fluor™

2-Amino alcohols and 1,2-diols treated with Deoxo-Fluor™ in methylene chloride resulted in the formation of rearranged major products concomitantly with minor amounts of the straightforward fluorinated replacement products in good yields.     

Chemoselective TBS deprotection of primary alcohols by means of pyridinium tribromide (Py·Br3) in MeOH

A catalytic amount of pyridinium tribromide (Py·Br₃) in MeOH chemoselectively deprotects primary TBS ethers in the presence of a variety of other protecting and common functional groups in modest to excellent yields when performed at 0 °C.     

Chemoselective reduction of β-butyltellanyl α,β-unsaturated carbonyl compounds to allylic alcohols

(Z)-β-Butyltellanyl α,β-unsaturated carbonyl compounds were stereoselectively produced by hydrotelluration of alkynones or by an addition/elimination sequence from enol tosylates. The β-butyltellanyl-enones were chemoselectively reduced with NaBH₄/MeOH, NaBH₄·CeCl₃·7H₂O/MeOH and DIBAL-H systems to the corresponding allylic alcohols with retention of the Z stereochemistry.     

Chemoselective tetrahydropyranylation of alcohols and phenols using polystyrene supported aluminium chloride as a catalyst

A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl₃. The method is also highly selective for monoprotection of symmetrical diols.     

Ionic liquids as recyclable solvents for diethylaminosulfur trifluoride (DAST) mediated fluorination of alcohols and carbonyl compounds

The first simple and efficient method for the synthesis of mono and gem-difluorinated molecules using [C₈mim][PF₆] ionic liquid as a recyclable solvent medium with diethylaminosulfur trifluoride (DAST) as the fluorinating reagent, is reported.     

Chemoselective organocatalytic aerobic oxidation of primary amines to secondary imines

Biomimetic aerobic oxidation of primary benzylic amines has been achieved by using a quinone catalyst. Excellent selectivity is observed for primary, unbranched benzylic amines relative to secondary/tertiary amines, branched benzylic amines, and aliphatic amines. The exquisite selectivity for benzylic amines enables oxidative self-sorting within dynamic mixtures of amines and imines to afford high yields of cross-coupled imine products.     

Chemoselective cross metathesis of bishomoallylic alcohols: rapid access to fragment a of the cryptophycins

[reaction: see text] The racemic or enantioselective allylation of in situ formed beta,gamma-unsaturated aldehydes provides efficient access to bishomoallylic alcohols from readily available 2-vinyloxiranes. These products, when subjected to modified Grubbs cross metathesis conditions, afforded terminally homologated products in moderate to good yields with high E selectivity and without degradation of the enantiomeric excess. The compounds obtained through this two-step sequence yield fragments of an important and pharmacologically active family of cryptophycins.     

Redox self-sufficient biocatalyst network for the amination of primary alcohols

Driving the machinery: A biocatalytic redox-neutral cascade for the preparation of terminal primary amines from primary alcohols at the expense of ammonia has been established in a one-pot one-step method. Applying this artificial biocatalyst network, long-chain 1,ω-alkanediols were converted into diamines, which are building blocks for polymers, in up to 99?% conversion.