Iodine-promoted five-component reaction using fragment assembly strategy to construct dihydrooxepines

An iodine-promoted fragment assembly strategy for the synthesis of fused heterocycles has been established. It provides an efficient route to construct pyrazolone-oxepine-pyrazoles from phenylhydrazines, aryl methyl ketones and acetoacetate esters. Notably, acetoacetate esters play two distinct pivotal roles in the five-component reaction by realizing the unique reactivities of methyl, methylene and carbonyl groups to construct 3-methyl-5-pyrazolone skeletons and by the reaction of methyl and carbonyl groups to form a C (sp3)-O bond.     

Divergent Synthesis of Vinyl‐, Benzyl‐, and Borylsilanes: Aryl to Alkyl 1,5‐Palladium Migration/Coupling Sequences

Organosilicon compounds have been extensively utilized both in industry and academia. Studies on the syntheses of diverse organosilanes is highly appealing. Through‐space metal/hydrogen shifts allow functionalization of C?H bonds at a remote site, which are otherwise difficult to achieve. However, until now, an aryl to alkyl 1,5‐palladium migration process seems to have not been presented. Reported herein is the remote olefination, arylation, and borylation of a methyl group on silicon to access diverse vinyl‐, benzyl‐, and borylsilanes, constituting a unique C(sp³)?H transformation based on a 1,5‐palladium migration process.     

Oxidation of Alkynyl Boronates to Carboxylic Acids,Esters, and Amides

A general efficient protocol was developed for the synthesis of carboxylic acids, esters, and amides through oxidation of alkynyl boronates, generated directly from terminal alkynes. This protocol represents the first example of C(sp)?B bond oxidation. This approach displays a broad substrate scope, including aryl and alkyl alkynes, and exhibits excellent functional group tolerance. Water, primary and secondary alcohols, and amines are suitable nucleophiles for this transformation. Notably, amino acids and peptides can be used as nucleophiles, providing an efficient method for the synthesis and modification of peptides. The practicability of this methodology was further highlighted by the preparation of pharmaceutical molecules.     

Strukturbestimmung von O-Methylazafrinmethylester durch 13C-NMR.-Spektroskopie

Structure Determination of Azafrin Methyl Ester 5-O-Monomethyl Ether by ¹³C-NMR.-Specta. The structure of the monomethyl ether ( 2 ) of azafrin methyl ester ( 1 ) was determined by a partial analysis of the ¹³C-NMR.-spectra. Assignments of quaternary carbon atoms and methyl groups in the cyclohexane ring were achieved using vicinal ¹³C-, ¹H-spin coupling. Substituent effects on methyl and methylene carbon atoms in 2 are discussed with respect to the conformation of the methoxy group. The spectra prove C(5)? OH as the site of methylation. Therefore C(5)? OH is less hindered than C(6)? OH.     

Carboxylate‐Assisted Oxidative Addition to Aminoalkyl PdII Complexes: C(sp3)−H Arylation of Alkylamines by Distinct PdII/PdIV Pathway

Reported is the discovery of an approach to functionalize secondary alkylamines using 2‐halobenzoic acids as aryl‐transfer reagents. These reagents promote an unusually mild carboxylate‐assisted oxidative addition to alkylamine‐derived palladacycles. In the presence of Ag^I salts, a decarboxylative C(sp³)?C(sp²) bond reductive elimination leads to γ‐aryl secondary alkylamines and renders the carboxylate motif a traceless directing group. Stoichiometric mechanistic studies were effectively translated to a Pd‐catalyzed γ‐C(sp³)?H arylation process for secondary alkylamines.     

Ligand‐Enabled PdII‐Catalyzed Iterative γ‐C(sp3)−H Arylation of Free Aliphatic Acid

C?H functionalization of aliphatic carboxylic acids without attaching exogenous auxiliary has been so far limited at the proximal β‐position. In this work, we demonstrate a ligand enabled palladium catalyzed first regioselective distal γ‐C(sp3)?H functionalization of aliphatic carboxylic acids without incorporating an exogenous directing group. Aryl iodides containing versatile functional groups including complex organic molecules are well tolerated with good to excellent yields during the γ‐C(sp3)?H arylation reaction. Interestingly, weak coordination of carboxylate group can be further extended for sequential hetero di‐arylation. Application of the protocol has been showcased by synthesizing substituted α‐tetralone. Mechanistic investigations have been carried out to shed light on the reaction pathway.     

Unusual group migration and C(sp3)-H activation leading to stable metallacycles in the reactions of Cp*IrS2C2B10H10 and aryl azides

The thermal or photochemical reactions of Cp*IrS(2)C(2)B(10)H(10) (1) and aryl azides lead to C-C coupling via C(sp(3))-H activation in 2 as well as the formation of C-S bonds and new-type SSN pincer ligands in 3-8 through ortho-substituted electron-withdrawing group migration over an aryl ring.     

Allenyl azide cycloaddition chemistry. synthesis of pyrrolidine-containing bicycles and tricycles via the possible intermediacy of azatrimethylenemethane species

Thermolysis of 5-azidoallenes bearing a C(1) methyl group and either an aryl ring or an alkene on C(1) furnishes tricyclic (from the aryl substrates) or bicyclic (from the alkenyl substrates) pyrrolidine products following formal H-CN addition across an intermediate imine. High levels of diastereoselectivity are observed in all cases studied. This reaction cascade presumably passes through unobserved triazoline and azatrimethylenemethane diyl intermediates en route to product.     

Asymmetric Synthesis of 1,3‐Butadienyl‐2‐carbinols by the Homoallenylboration of Aldehydes with a Chiral Phosphoric Acid Catalyst

Asymmetric C(sp)? C(sp²) bond formation to give enantiomerically enriched 1,3‐butadienyl‐2‐carbinols occurred through a homoallenylboration reaction between a 2,3‐dienylboronic ester and aldehydes under the catalysis of a chiral phosphoric acid (CPA). A diverse range of enantiomerically enriched butadiene‐substituted secondary alcohols with aryl, heterocyclic, and aliphatic substituents were synthesized in very high yield with high enantioselectivity. Preliminary density functional theory (DFT) calculations suggest that the reaction proceeds via a cyclic six‐membered chairlike transition state with essential hydrogen‐bond activation in the allene reagent. The catalytic reaction was amenable to the gram‐scale synthesis of a chiral alkyl butadienyl adduct, which was converted into an interesting optically pure compound bearing a benzo‐fused spirocyclic cyclopentenone framework.     

Development of Modifiable Bidentate Amino Oxazoline Directing Group for Pd‐Catalyzed Arylation of Secondary CH Bonds

A novel bidentate α‐amino oxazolinyl directing group has been developed. Different from previous directing groups, this newly designed directing group was easily prepared from amino acids and modified in structure. This auxiliary preferentially effects functionalization at secondary C(sp³)?H bonds, rather than at aryl C(sp²)?H bonds. The diastereoselectivity of direct arylation between geminal secondary C(sp³)?H bonds in linear molecules has also been realized for the first time with a chiral directing group by remote chirality relay. Two diastereoisomers are produced with the same chiral source by changing the substituents of substrates and aryl halides.     

Oxidative Addition of Carbon–Carbon Bonds to Gold

The oxidative addition of strained C? C bonds (biphenylene, benzocyclobutenone) to DPCb (diphosphino‐carborane) gold(I) complexes is reported. The resulting cationic organogold(III) complexes have been isolated and fully characterized. Experimental conditions can be adjusted to obtain selectively acyl gold(III) complexes resulting from oxidative addition of either the C(aryl)? C(O) or C(alkyl)? C(O) bond of benzocyclobutenone. DFT calculations provide mechanistic insight into this unprecedented transformation.     

Photochemical Reactions. 153th communication. Photochemistry of acylsilanes: Photolyses and thermolyses of α,β-epoxy silyl ketones

The photolyses and thermolyses of the α,β-epoxy silyl ketones 5 and 6 are described. On n,π*-excitation, the silyl ketones 5 and 6 were transformed to the ketone 7 and the ketene 8 in quantitative yield. The formation of 8 may be explained by initial cleavage of the C(α)? O bond and subsequent C(1)→C(2) migration of the (t-Bu)Me₂Si group. In contrast to the acylsilanes 5 and 6 , the photolyses of the analogous methyl ketones 11 and 12 gave a very complex mixture of products. On thermolysis, 5 and 6 yielded the ketone 7 and the acetylenic compound 9 , which were probably formed via a siloxycarbene intermediate. In addition, the 1,3-dioxle 10 was formed via an initial C(α)? C(β) bond cleavage leading to the ylide g and subsequent intramolecular addition of the carbonyl group. The analogous 1,3-dioxole 13 was obtained on pyrolysis of the methyl ketones 11 and 12 .     

Readily Removable Directing Group Assisted Chemo‐ and Regioselective C(sp3)H Activation by Palladium Catalysis

Currently used directing groups for selective aliphatic β‐functionalization of carbonyl compounds show excellent reactivity and selectivity with an amide as a linker. Described herein is 2‐piconimide, used for the first time with commercially available 2‐picolinamide/2‐picolic acid as precursors, to direct C? H arylation/alkenylation by palladium catalysis. The directing group is essential for promoting the sequnetial primary and secondary C(sp³)? H arylation with different aryl iodides in one substrate. The directing group was easily removed under simple reaction conditions at room temperature.     

Rhodium(III)‐Catalyzed [3+2] Annulation of 5‐Aryl‐2,3‐dihydro‐1H‐pyrroles with Internal Alkynes through C(sp2)H/Alkene Functionalization

This study describes a new rhodium(III)‐catalyzed [3+2] annulation of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles with internal alkynes using a Cu(OAc)₂ oxidant for building a spirocyclic ring system, which includes the functionalization of an aryl C(sp²)? H bond and addition/protonolysis of an alkene C?C bond. This method is applicable to a wide range of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles and internal alkynes, and results in the assembly of the spiro[indene‐1,2′‐pyrrolidine] architectures in good yields with excellent regioselectivities.     

Diphenyl disulfide and sodium in NMP as an efficient protocol for in situ generation of thiophenolate anion: selective deprotection of aryl alkyl ethers and alkyl/aryl esters under nonhydrolytic conditions

Aryl methyl ethers, methyl esters, aryl esters, and aryl sulfonates are chemoselectively deprotected under nonhydrolytic conditions by treatment with Ph(2)S(2) (0.6 equiv) and Na (1.6 equiv) in NMP under reflux or at 90 degrees C. Quantitative utilization of the 'PhS' moiety as the effective nucleophilic species represents conservation of atom economy. Other solvents such as HMPA, DMPU, DMEU, and DMF afforded comparable results. Chloro, nitro, aldehyde, alpha,alpha-diketone, and alpha,beta-unsaturated ketone functionalities remain unaffected. The deprotection was found to take place in the order aryl ester > alkyl ester > aryl alkyl ether. Substrates bearing strong electron-withdrawing groups react at a faster rate than those not having such substitution. The differences in rate of reaction has been exploited for selective deprotection for intramolecular competition. An aryl acetate/benzoate is deprotected selectively in preference to a methyl ester or aryl methyl ether. Selective deprotection of a methyl ester is observed in the presence of an aryl alkyl ether.     

Umsetzungen des Tetrakis[bis(trimethylsilyl)methyl]dialans(4) mit Methylisothiocyanat und Phenylisocyanat – Insertion in die Al?Al-Bindung bzw. Fragmentierung

Reactions of Tetrakis[bis(trimethylsilyl)methyl]dialane(4) with Methylisothiocyanate and Phenylisocyanate – Insertion into the Al? Al Bond and Fragmentation Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacts with methyl isothiocyanate under cleavage of the C?S double bond and insertion of the remaining isonitrile fragment into the Al? Al bond. As shown by crystal structure determination a three-membered AlCN heterocycle ( 4 ) is formed by the interaction of the nitrogen lone pair with one unsaturated Al atom leading to an acute angle at the aluminium center N? Al? C of 36.6°. In contrast the reaction with the hard base phenyl isocyanate yields a mixture of many unknown compounds, from which only one ( 5 ) could be isolated in a very poor yield. The crystal structure of 5 reveals only one dialkyl aluminium fragment and a chelating ligand formed by the trimerization of the isocyanate under loss of one CO group and addition of a hydrogen atom. 5 was also synthesized by the specific reaction of the chloro dialkyl aluminium compound (R = CH(SiMe₃)₂) with Li[H₅C₆? N?C(O)? N(C₆H₅)? C(O)? N(H)? C₆H₅].     

Copper‐Catalyzed Aerobic Oxidative CC Bond Cleavage for CN Bond Formation: From Ketones to Amides

A novel copper‐catalyzed aerobic oxidative C(CO)? C(alkyl) bond cleavage reaction of aryl alkyl ketones for C? N bond formation is described. A series of acetophenone derivatives as well as more challenging aryl ketones with long‐chain alkyl substituents could be selectively cleaved and converted into the corresponding amides, which are frequently found in biologically active compounds and pharmaceuticals.     

Diastereoselective approach to 11-aryl steroid skeletons through a cobalt(I)-mediated [2+2+2] cyclization of allenediynes

The cobalt(I)-mediated [2+2+2] cycloaddition reactions of allenediynes of yne-allene-yne type bearing an aryl group on the allene are described. The cyclizations are totally chemo- and regioselective and show low diastereoselectivities. η⁴-Complexed tricyclic (6,6,6) compounds were obtained in good yields as mixtures of endo/exo diastereomers. The cyclization is also compatible with an oxyfunctionality at C3. By designing an allenediyne having a preexisting D ring, we succeeded in building skeletons of 11-aryl steroids in one step and in a totally diastereoselective manner and with simultaneous introduction of an angular methyl group at C10 and an aryl substituent at C11.     

2,4‐Dinitrophenol‐Catalyzed α‐C(sp3)−H and C(sp)−H Bond Functionalization of Cyclic Amines and Alkynes: Highly Regio‐/Diastereoselective Synthesis of α‐Alkynyl‐3‐Amino‐2‐Oxindoles

A transition‐metal‐ and oxidant‐free DNP (2,4‐dinitrophenol)‐catalyzed atom‐economical regio‐ and diastereoselective synthesis of monofunctionalized α‐alkynyl‐3‐amino‐2‐oxindole derivatives by C?H bond functionalization of cyclic amines and alkynes with indoline‐2,3‐diones has been developed. This cascade event sequentially involves the reductive amination of indoline‐2,3‐dione by imine formation and cross coupling between C(sp³)?H and C(sp)?H of the cyclic amines and alkynes. This reaction offers an efficient and attractive pathway to different types of α‐alkynyl‐3‐amino‐2‐oxindole derivatives in good yields with a wide tolerance of functional groups. The salient feature of this methodology is that it completely suppresses the homocoupling of alkynes. To the best of our knowledge, this is the first example of a DNP‐catalyzed metal‐free direct C(sp³)?H and C(sp)?H bond functionalization providing biologically active α‐alkynyl‐3‐amino‐2‐oxindole scaffolds.     

Di‐tert‐Butyl Peroxide‐Mediated Atom‐Transfer Radical Addition of 2‐Chlorodithiane to Aryl Alkynes under Mild Conditions

Atom transfer radical addition (ATRA) of 2‐chlorodithiane onto aryl alkynes through the use of di‐tert‐butyl peroxide as an oxidant at room temperature directly affords a variety of synthetically valuable β‐chloro‐(Z)‐vinyl dithianes in good yields with high regioselectivities and without the assistance of any transition metals. It provides an operationally simple pathway to access vinyl dithianes with controlled formation of a new C(sp²)?C bond and a C(sp²)?Cl bond.