Unexpected copper-catalyzed aerobic oxidative cleavage of C(sp3)-C(sp3) bond of glycol ethers

An unexpected Cu-catalyzed oxidative cleavage of the C(sp(3))-C(sp(3)) bond in glycol ethers by using air or molecular oxygen as the terminal stoichiometric oxidant is demonstrated. As a result, the corresponding α-acyloxy ethers and formates of 1,2-ethanediol are formed by direct coupling of carboxylic acids and aldehydes with glycol ethers under the reaction conditions. This method represents the first example of Cu-catalyzed aerobic cleavage of saturated C-C bond in ethers.     

Facile copper-mediated activation of the N-H bond and the oxidative cleavage of the C2-C3 bond in 1H-2-phenyl-3-hydroxy-4-oxoquinoline

The reaction of 1H-2-phenyl-3-hydroxy-4-oxoquinoline (PhquinH(2); 1) with metallic copper leads to Cu(II)(PhquinH)(2) while in the presence of PPh(3) to Cu(I)(2)Cu(II)(Phquin)(2)(PPh(3))(4). In the presence of tmeda and O(2) ring cleavage occurs to give Cu(II)(tmeda)(PhquinH)(N-baa). Both reactions represent a mild N-H activation and an oxidative C-C bond scission.     

Iron-catalyzed C2-C3 bond cleavage of phenylpyruvate with O2: insight into aliphatic C-C bond-cleaving dioxygenases

Iron(II)-phenylpyruvate complexes of tetradentate tris(6-methyl-2-pyridylmethyl)amine (6-Me3-TPA) and tridentate benzyl bis(2-quinolinylmethyl)amine (Bn-BQA) were prepared to gain insight into C-C bond cleavage catalyzed by dioxygenase enzymes. The complexes we have prepared and characterized are [Fe(6-Me3-tpa)(prv)][BPh4] (1), [Fe2(6-Me3-tpa)2(pp)][(BPh4)2] (2), and [Fe2(6-Me3-tpa)2(2'-NO2-pp)][(BPh4)2] (3), [Fe(6-Me3-tpa)(pp-Me)][BPh4] (4), [Fe(6-Me3-tpa)(CN-pp-Et)][BPh4] (5), and [Fe(Bn-bqa)(pp)] (8), in which PRV is pyruvate, PP is the enolate form of phenylpyruvate, 2'-NO2-PP is the enolate form of 2'-nitrophenylpyruvate, PP-Me is the enolate form of methyl phenylpyruvate, and CN-PP-Et is the enolate form of ethyl-3-cyanophenylpyruvate. The structures of mononuclear complexes 1 and 5 were determined by single-crystal X-ray diffraction. Both the PRV ligand in 1 and the CN-PP-Et ligand in 5 bind to the iron(II) center in a bidentate manner and form 5-membered chelate rings, but the alpha-keto moiety is in the enolate form in 5 with concomitant loss of a C-H(beta) proton. The PP ligands of 2, 3, 4, and 8 react with dioxygen to form benzaldehyde and oxalate products, which indicates that the C2-C3 PP bond is cleaved, in contrast to cleavage of the C1-C2 bond previously observed for complexes that do not contain alpha-ketocarboxylate ligands in the enolate form. These reactions serve as models for metal-containing dioxygenase enzymes that catalyze the cleavage of aliphatic C-C bonds.     

Photooxygenation of the CN bond: a mild new method for oxidative CC cleavage

Upon photooxygenation in the presence of base, α-oximinocarbonyl compounds undergo clean oxidative CC cleavage giving rise to mixtures of esters and acids. The mechanism of these reactions involves some unusual peroxidic intermediates, including a 2,3,5-trioxapentanes.     

I2-Catalyzed enantioselective ring expansion of beta-lactams to gamma-lactams through a novel C3-C4 bond cleavage. Direct entry to protected 3,4-dihydroxypyrrolidin-2-one derivatives

Molecular iodine (10 mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert-butyldimethyl cyanide to afford protected 5-cyano-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a novel C3-C4 bond cleavage of the beta-lactam nucleus.     

Efficient 2-aryl benzothiazole formation from acetophenones,anilines, and elemental sulfur by iodine-catalyzed oxidative C(CO)-C(alkyl) bond cleavage

A novel and efficient iodine-catalyzed one-pot reaction of aromatic amines, acetophenones, and elemental sulfur for the synthesis of 2-aryl benzothiazoles is described. The process involves sequential C?S and C-N bond formation followed by C(CO)?C bond cleavage from readily accessible starting materials. A wide range of functional groups is tolerated under oxidant and metal-free condition and moderate to good product yields are obtained.     

Unexpected oxidative C-C cleavage in the metallation of 2-substituted imidazolium salts to give N-heterocyclic carbene complexes

Imidazolium salts blocked at C2 with methyl or benzyl groups unexpectedly react with silver oxide to give N-heterocyclic carbene complexes of silver via an oxidative carbon-carbon bond cleavage.     

Unexpected cleavage of the N-N bond in the reactions of 3-pyrazolidinone-1-azomethine imines with HCN

Treatment of (1Z,4R^∗,5R^∗)-1-arylmethylidene-4-benzamido-5-phenylpyrazolidin-3-one 1-azomethine imines 4a-d with potassium cyanide in the presence of acetic acid resulted in addition of HCN to the exocyclic CN double bond followed by β-eliminative N-N single bond cleavage (ring opening) to give the N-[(1R^∗,2R^∗)-3-amino-2-benzamido-3-oxo-1-phenylpropyl]benzimidoyl cyanides 6a-d in 28-85% yields. Reaction of dipole 4e with HCN furnished stable intermediate, (1′S^∗,4R^∗,5R^∗)-4-benzamido-1-[cyano(mesityl)methyl]-5-phenylpyrazolidin-3-one (5e), in 76% yield. The structure of compound 6c was determined by X-ray diffraction.     

Synthesis of nine-, ten-, and fifteen-membered alkenolides by the oxidative cleavage of the bridging C=C bond in 2-oxabicycloalkenes

Hydroperoxidation of C=C-bridged 2-oxabicycloalkenes in which the five- or six-membered oxacycle is fused with the five-, six-, or twelve-membered hydrocarbon ring was studied. The Cu(OAc)₂-catalyzed decomposition of the resulting hydroperoxides afforded nine-, ten-, or fifteen-membered trans-alkenolides, respectively. The latter compounds were obtained as pairs of regioisomers, with the isomers in which the double bond is more remote from the ether oxygen atom predominating.     

Photochemistry of 2-nitrobenzyl enol ethers: oxidative C=C bond scission

[reaction: see text] 2-Nitrobenzyl enol ethers, when photolyzed in the presence of air, result in an oxidative C=C bond scission, forming a ketone as the major product (>60% yield). Enol release leads to the aldehyde as the minor product.     

Chemical and transient spectroscopic evidence for C2-C3 cleavage of 2,3-diaryloxetane radical cations

Electron transfer cycloreversion of the methoxy substituted oxetane 1b results in the production of trans-anethole and benzaldehyde through C2-C3 bond cleavage. trans-Anethole radical cation has been detected as transient intermediate by laser flash photolysis.     

A non-classical hydrogen bond in the molybdenum arene complex [eta 6-C6H5C6H3(Ph)OH]Mo(PMe3)3: evidence that hydrogen bonding facilitates oxidative addition of the O-H bond

Mo(PMe3)6 reacts with 2,6-Ph2C6H3OH to give the eta 6-arene complex [eta 6-C6H5C6H3(Ph)OH]Mo(PMe3)3 which exhibits a non-classical Mo...H-OAr hydrogen bond; DFT calculations indicate that the hydrogen bonding interaction facilitates oxidative addition of the O-H bond to give [eta 6,eta 1-C6H5C6H3(Ph)O]Mo(PMe3)2H.     

Access to C(sp3)-C(sp2) and C(sp2)-C(sp2) bond formation via sequential intermolecular carbopalladation of multiple carbon-carbon bonds

A synthetic strategy of 4-benzyl-substituted 1,3-butadiene derivatives through Pd-catalyzed three-component coupling reaction of benzyl chlorides, alkynes, and monosubstituted alkenes is described. This tandem coupling reaction forms a C(sp(3))-C(sp(2)) bond and a C(sp(2))-C(sp(2)) bond sequentially in a single-step operation.     

Pectenotoxin-2 synthetic studies. 3. Assessment of the capacity for stereocontrolled cyclization to form the entire C1-C26 subunit based upon the double bond geometry across C15-C16

Second-generation synthetic routes to enantiopure sulfone 21 and aldehyde 24 are described. The union of these two intermediates by means of a Julia-Kocienski coupling gave rise to a series of E-configured building blocks that did not prove amenable to transannular cyclization. Alternatively, when the C15-C16 double bond was introduced with Z-geometry by Wittig olefination, spontaneous closure to generate a tetrahydrofuran culminated an ensuing direct dihydroxylation step. The structural assignment to 35, undergirded by detailed 1H and 13C NMR studies, is consistent with proper transannular bonding so as to deliver the entire C1-C26 fragment of PTX2.     

Unexpected oxidation of a substituted benzo[a]phenazine: oxidative cleavage of a double bond and formation of a macrolactone

Peroxidation of the phenazine of β-lapachone using m-ClC₆H₄CO₃H/CH₂Cl₂ furnished a macrolactone with a rigid 10-membered ring, and the corresponding N-oxide, originating from the oxidative cleavage of the aromatic double bond at the site of fusion of the dihydropyrane moiety with the phenazine component. A third compound, a dihydrobenzophenazine-5-one, was also generated probably by hydrolysis of an intermediate epoxide-acetal or α-hydroxy-hemiacetal formed at the same site. All of the new compounds were fully characterized by X-ray diffractometry and spectroscopic methods.     

Unusual cyclopropanation of 9-bromocamphor derivatives: a novel formal C(1)-C(7) bond cleavage of camphor

[reaction: see text] An unusual cyclopropanation of 9-bromocamphor derivatives 1 to a 7-spiro-cyclopropyl camphor derivative 3 was effected by the action of potassium tert-butoxide (or sodium hydride) in warm DMSO. The exo-hydroxy group and a non-hydrogen endo-substituent at C(2) have proven to be essential structural elements, and the solvent DMSO has proven to be the sole effective reaction medium. Tricyclic compound 3 undergoes a facile tandem Wagner-Meerwein rearrangement-cyclopropyl ring-opening under mild acidic conditions, leading to norbornenyl derivative 12 and subsequent Meinwald rearrangement of bicyclic epoxide 13 to a formal C(1)-C(7) bond cleavage product 14.     

Chemistry of trichosanthin: VII. The chemical cleavage of the tryptophanyl peptide bond in trichosanthin

The single tryptophan residue of trichosanthin was cleaved by the use of BNPS-skatole reaction with STIG2 peptide fregment which was obtained from the tryptic digestion of N-succinyl trichosanthin. After separation, the N-terminal sequence of tryptophanyl C-side peptide was determined by use of manual DABITC-PITC double coupling sequencing method as follows: -Leu-Ala-Leu-Ser-Lys-Gln-Ile-Gln-Ile-Ala-.