Tertiary Alcohol Derivatives Research Articles

Green Chemistry Approach toward the Regioselective Synthesis of α,α-Disubstituted Allylic Amines.

Molybdenum-catalyzed allylic substitution reactions are known to provide direct and practical ways to construct new carbon-carbon bonds and privileged compounds. However, due to the lack of reports on carbon-heteroatom bond formation as a common deficiency, these reactions still face a great challenge. Described herein is a robust and convenient molybdenum-catalyzed regioselective allylic amination of tertiary allylic carbonates with an amine as the heteroatom nucleophile. Both aromatic and aliphatic amines react with various tertiary allylic alcohol derivatives to deliver the desired α,α-disubstituted allylic amines in high yield with complete regioselectivity. In addition, ethanol as the green solvent, a recyclable catalyst system through simple centrifugation techniques, and simple handling procedures make the current approach green, economic, and sustainable.

Visible Light-Mediated Enantioselective Addition of α-Aminoalkyl Radicals to Ketones Catalyzed by Chiral Oxazaborolidinium Ion.

The development of a visible light-mediated synthetic method for chiral 1,2-amino tertiary alcohols is described. In the presence of a chiral oxazaborolidinium ion catalyst and photosensitizer, the enantioselective addition of an α-aminoalkyl radical to aryl methyl ketones under visible light provides chiral 1,2-amino tertiary alcohol derivatives in high yields (up to 88%) with excellent enantioselectivities (up to 98% ee). With mechanistic studies such as radical trapping analysis, radical clock analysis, and the measurement of quantum yield, a plausible catalytic cycle is proposed.

Synthesis of Fluorinated Tertiary Alcohol Derivatives under Visible-Light Irradiation

Synthesis of Fluorinated Tertiary Alcohol Derivatives under Visible-Light Irradiation

Reductive Activation and Hydrofunctionalization of Olefins by Multiphoton Tandem Photoredox Catalysis

The conversion of olefin feedstocks to architecturally complex alkanes represents an important strategy in the expedient generation of valuable molecules for the chemical and life sciences. Synthetic approaches are reliant on the electrophilic activation of unactivated olefins, necessitating functionalization with nucleophiles. However, the reductive functionalization of unactivated and less activated olefins with electrophiles remains an ongoing challenge in synthetic chemistry. Here, we report the nucleophilic activation of inert styrenes through a photoinduced direct single electron reduction to the corresponding nucleophilic radical anion. Central to this approach is the multiphoton tandem photoredox cycle of the iridium photocatalyst [Ir(ppy)2(dtbbpy)] PF6, which triggers in situ formation of a high-energy photoreductant that selectively reduces styrene olefinic π bonds to radical anions without stoichiometric reductants or dissolving metals. This mild strategy enables the chemoselective reduction and hydrofunctionalization of styrenes to furnish valuable alkane and tertiary alcohol derivatives. Mechanistic studies support the formation of a styrene olefinic radical anion intermediate and a Birch-type reduction involving two sequential single electron transfers. Overall, this complementary mode of olefin activation achieves the hydrofunctionalization of less activated alkenes with electrophiles, adding value to abundant olefins as valuable building blocks in modern synthetic protocols.

Fluorinated Ketones as Trapping Reagents for Visible-Light-Induced Singlet Nucleophilic Carbenes.

Singlet nucleophilic carbenes (SNCs) containing only one heteroatom donor remain underutilized in chemical synthesis. We recently discovered that visible-light-induced SNC intermediates can be trapped by fluorinated ketones via 1,2-carbonyl addition to afford benzoin-type products. This discovery represents a rare example of nucleophilic carbenes reacting with ketones and delivers an efficient, user-friendly, and scalable process for accessing fluorinated tertiary alcohol derivatives driven only by light circumventing the use of exogenous catalysts or additives.

Visible‐Light‐Promoted Regio‐ and Stereoselective Oxyalkenyl‐ation of Phosphinyl Allenes

AbstractA highly regio‐ and stereoselective oxyalkenylation of phosphinyl allenes is revealed for the first time. This protocol, merging visible light photoredox and palladium catalysis, provides a direct approach to conjugated tertiary allylic alcohol derivatives with broad functional group tolerance in moderate to excellent yields. Mechanistic studies suggest that, although two possible pathways exist in the transformation, radical oxyalkenylation promoted by visible light photoredox takes over the major pathway.magnified image

Light-Mediated Formal Radical Deoxyfluorination of Tertiary Alcohols through Selective Single-Electron Oxidation with TEDA2+.

The synthesis of tertiary alkyl fluorides through a formal radical deoxyfluorination process is described herein. This light‐mediated, catalyst‐free methodology is fast and broadly applicable allowing for the preparation of C−F bonds from (hetero)benzylic, propargylic, and non‐activated tertiary alcohol derivatives. Preliminary mechanistic studies support that the key step of the reaction is the single‐electron oxidation of cesium oxalates—which are readily available from the corresponding tertiary alcohols—with in situ generated TEDA2+. (TEDA: N‐(chloromethyl)triethylenediamine), a radical cation derived from Selectfluor®.

Controllable Intramolecular Unactivated C(sp3)-H Amination and Oxygenation of Carbamates.

Dual catalyst-controlled intramolecular unactivated C(sp3)-H amination and oxygenation of carbamates merging visible-light photocatalysis and earth-abundant transition metal catalysis have been reported. Useful amino alcohol and diol derivatives could be selectively obtained from readily available tertiary alcohol derivatives. The possible mechanisms have been proposed via a 1,5-HAT process followed by Lewis acid-controlled cyclization. The nickel and zinc catalysts inhibit the formation of oxygenation and amination products, respectively. An interesting phenomenon of chirality transfer is also observed.

Cu(II)-Catalyzed Enantioselective β-Boration of β-Trifluoromethyl, β,β-Disubstituted Enones and Esters: Construction of a CF3- and Boron-Containing Quaternary Stereocenter

A highly enantioselective Cu(II)-catalyzed borylative reaction of β-trifluoromethyl β,β-disubstituted enones was developed, which provide a facile access to a variety of chiral alkylboronic esters with a quaternary stereocenter including both a trifluoromethyl group and a boron group. Meanwhile, CF3-contained tertiary alcohol derivatives were obtained in high yield with the maintained ee value via one-pot methodology. The reactions proceed smoothly under mild reaction conditions, providing expedient access to construct chiral alkylboronic esters in well-functional group tolerances, good yields, diversity conversion, and high enantioselectivities. The appropriate SDE test via achiral chromatography illustrated that the results presented here were reliable.

Catalytic enantioselective radical coupling of activated ketones with N-aryl glycines.

Asymmetric H-bonding catalysis as a viable strategy for enantioselective radical coupling of ketones is demonstrated. With a visible-light-mediated dual catalytic system involving a dicyanopyrazine-derived chromophore (DPZ) photosensitizer and a chiral phosphoric acid (CPA), N-aryl glycines with a variety of 1,2-diketones and isatins underwent a redox-neutral radical coupling process and furnished two series of valuable chiral 1,2-amino tertiary alcohols in high yields with good to excellent enantioselectivities (up to 97% ee). In this catalysis platform, the formation of neutral radical intermediates between ketyl and H-bonding catalyst CPA is responsible for presenting stereocontrolling factors. Its success in this work should provide inspiration for expansion to other readily accessible ketones to react with various radical species, thus leading to a productive approach to access chiral tertiary alcohol derivatives.

Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aliphatic Ketones: Synthesis of Enantioenriched Chiral Tertiary α-Hydroxyboronates.

A new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex catalyst to furnish optically active tertiary α-hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described.

Copper(I)‐Catalyzed Enantioselective Nucleophilic Borylation of Aliphatic Ketones: Synthesis of Enantioenriched Chiral Tertiary α‐Hydroxyboronates

AbstractA new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N‐heterocyclic carbene complex catalyst to furnish optically active tertiary α‐hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described.

Stereospecific Cross Couplings To Set Benzylic, All-Carbon Quaternary Stereocenters in High Enantiopurity.

Asymmetric preparation of all-carbon quaternary stereocenters is an important goal. Despite advances in formation of highly enantioenriched products with quaternary stereocenters proximal to a functional group, methods to install quaternary stereocenters isolated from functional groups are limited. Transition metal catalysis offers a potential solution, but prior cross couplings are limited to allylic substrates or deliver little to no enantiomeric enrichment. We report a stereospecific, nickel-catalyzed Suzuki–Miyaura arylation of tertiary benzylic acetates to deliver products with diaryl and triaryl quaternary stereocenters in high yields and ee’s. This reaction employs an inexpensive, air-stable Ni(II) salt and commercially available phosphine ligand to transform tertiary alcohol derivatives, which are easily available in exceptional ee, into valuable products with stereoretention.

Further Explorations into the Synthesis of Dehydro‐Hedione®

AbstractDehydrohedione (DHH) 1 may be obtained in 20% overall yield by a Reformatsky reaction with enone methyl ether 3b, followed by acidic workup of the crude reaction mixture. Alternatively, epoxidation (3‐chloroperbenzoic acid, CH2Cl2, 84% yield) of the tertiary allyl alcohol derivative 4 affords a 1 : 2 mixture of 8a and 8b. The latter epoxy ester 8b may also be obtained stereoselectively either from 4 (tBuO2H, [Mo(CO)6], 1,2‐dichloroethane, 70°, 62% yield; or tBuO2H, [VO(acac)2], decane, 20°, 92% yield), or from 5 (AcOMe, LiN(SiMe3)2, THF, −78°, 84–87%). BF3⋅Et2O‐Catalyzed cascade rearrangement and OH elimination of 8a afford selectively DHH 1 in 88% yield. The cis disposition of the side chains of the weakly odoriferous hedione‐like analogues 2b and 2c was maintained by means of either an epoxy or a cyclopropane moiety.

Rhodium-Catalyzed Allylic Substitution with an Acyl Anion Equivalent: Stereospecific Construction of Acyclic Quaternary Carbon Stereogenic Centers

A highly regio- and stereospecific rhodium-catalyzed allylic alkylation of tertiary allylic alcohol derivatives with a cyanohydrin pronucleophile is described. This direct and operationally simple protocol provides a fundamentally novel approach toward the synthesis of α-quaternary substituted ketones and circumvents many of the inherent problems associated with conventional enolate alkylation reactions. The stereospecific variant of this reaction provides the enantiomerically enriched α-quaternary substituted allylic aryl ketone, which is a particularly challenging intermediate for more conventional enolate-based strategies.

Inherently Chiral Cyano‐Substituted Resorcin[4]arene: A Promising Starting Point for Further Functionalization

AbstractAn inherently chiral cyano‐substituted resorcin[4]arene has been prepared by palladium‐catalyzed cyanation. Based on this reaction, the four cyano groups were converted into ketones, aldehydes, amides, and amines. The ketone derivative was converted into the corresponding macrocycle with four tertiary alcohol functionalities. Furthermore, demethylation of the methoxy groups to give the phenol groups was carried out in the presence of the keto groups. Single‐crystal X‐ray analysis was performed with the cyano, ketone, tertiary alcohol, and phenol compounds. Changing the methoxy to a phenoxy group also led to a distinct modification of the molecular assembly in the solid state. A study of the tertiary alcohol derivative thereby revealed a remarkable twist of the C2‐symmetrical molecule.

A Three-Step Synthetic Approach to Asymmetrically Functionalized 4H-Cyclopenta[2,1-b:3,4-b′]dithiophenes

A convenient and efficient three-step route toward both symmetrically and asymmetrically functionalized 4H-cyclopenta[2,1-b:3,4-b']dithiophenes has been developed. Using this method a broad collection of functionalized bridged bithiophenes can smoothly be accessed. Starting from 3-bromo-2,2'-bithiophene, prepared by Kumada coupling of 2-thienylmagnesium bromide with 2,3-dibromothiophene under Pd(dppf)Cl(2) catalysis, lithiation and subsequent reaction with dialkyl ketones afforded (a)symmetrically dialkylated tertiary alcohol derivatives. By means of final Friedel-Crafts dehydration cyclization in sulfuric acid medium, these derivatives were converted to 4,4-dialkyl-4H-cyclopenta[2,1-b:3,4-b']dithiophenes. Upon replacement of the dialkyl ketone reagent by ethyl levulinate, an ester-functionalized 4H-cyclopenta[2,1-b:3,4-b']dithiophene was prepared, representing an attractive precursor for variously functionalized cyclopentadithiophene compounds.

Formation of chiral tertiary homoallylic alcohols via Evans aldol reaction or enzymatic resolution and their influence on the Sharpless asymmetric dihydroxylation

Enantioenriched tertiary homoallylic alcohol derivatives ( S)- 2c and ( S)- 2a were obtained via Evans aldol methodology and enzymatic resolution of racemic tertiary acetate 2e, respectively. In order to study asymmetric 1,3-induction of the stereogenic center present in 2, congener ( R)- 2a as well as its O-protected derivatives ( R)- 2b– d were submitted to Sharpless asymmetric dihydroxylation to yield the diastereomeric 1,2,4-triol derivatives (2 R,4 R)- and (2 S,4 R)- 3a– d, revealing that neither the substrate nor the Sharpless catalyst exert any stereocontrol. Similar observations were made for the less bulky alkynyl-substituted derivative 12b. However, by using a directed dihydroxylation, the anti product (2 R,4 R)- 3a was favored.

Novel synthetic route for 5‐substituted 6‐arylmethylluracils from 2,4,6‐trichloropyrimidines

Abstract magnified image Treatment of 2,4,6‐trichloropyrimidines (1a, 1b) with the sodium salt of benzyl cyanide derivatives (2a, 2b) afforded 5‐substituted 4‐aryl(cyanomethyl)‐2,6‐dichloropyrimidines (3a, 3b, 3c, 3d, 3e, 3f). Compounds 3a, 3b were alkylated with methyl iodide to furnish 4‐(1‐aryl‐1‐cyanoethyl)‐2,6‐dichloropyrimidines (4a, 4b). Compounds 3a, 3b, 3c, 3d, 3e, 3f and 4a, 4b were hydrolyzed with concentrated hydrochloric acid to afford 5‐substituted 6‐arylalkyluracils 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h. 5‐Bromo‐6‐arymethylluracils (6a, 6b, 6c, 6d) were synthesized by bromination of 6‐arylmethylluracils (5a, 5b, 5c, 5d) with N‐bromosuccinimide (NBS). Refluxing 2‐(2,6‐dichloro‐5‐ethylpyrimidin‐4‐yl)‐2‐(3,5‐dimethylphenyl)acetonitrile (3f) with sodium methoxide followed by oxidation afforded (3,5‐dimethylphenyl)(5‐ethyl‐2,6‐dimethoxypyrimidin‐4‐yl)methanone (7). Addition of methylmagnesium bromide to compound 7 gave the tertiary alcohol derivative 8 which was fluorinated by diethylaminosulfurtrifluoride and deprotected by trimethylsilyl iodide to furnish 6‐(1‐(3,5‐dimethylphenyl)‐1‐fluoroethyl)‐5‐ethylpyrimidine‐2,4(1H,3H)‐dione (12). J. Heterocyclic Chem., (2009).

Synthesis of Two New Hemisynthetic Diterpenylhydroquinones from Natural Ent-Labdanes

The synthesis and structural determination of two new diterpenylhydroquinones: 2β-acetoxy-15-phenyl-(22,25-dihydroxy)-ent-labda-8(17),13(E)-diene (1) and 2β-hydroxy-15-phenyl-(22,25-dihydroxy)-ent-labda-8(17),13(E)-diene is reported (2). These compounds were obtained by coupling via Electrophilic Aromatic Substitution (EAS) of 1,4-hydroquinone with primary or tertiary allyl alcohol derivatives of the natural ent-labdanes 3 and 4. With this new method, the best results were observed when mixtures of the primary alcohol derivatives 5-6 (26% yield of compound 1) and diol derivatives 9-10 (28% yield of compound 2) were used.