Photomediated synthesis of β-alkylketones from cycloalkanes

β-Cycloalkylketones are prepared through a photomediated radical addition reaction onto enones starting from the corresponding alkanes (i.e., cyclopentane, -hexane, -heptane, -dodecane and adamantane). The alkyl radicals are generated via hydrogen abstraction by either an organic (benzophenone) or an inorganic (tetrabutylammonium decatungstate, TBADT) photomediator. Isolated yields vary in the range 30-80%. Benzophenone has to be considered as a reagent, since it is used in an equimolar amount with respect to enone and is completely consumed in the reaction. On the contrary, TBADT is shown to behave as a photocatalyst, which is active for at least 50 cycles. The potential of photomediated reactions for the generation of radicals from unusual precursors and the synthetic significance of this method are discussed.     

(3-Hydroxy-3-methylbutyn-1-yl)cycloalkan-1-ols in the Ritter Reaction

(3-Hydroxy-3-methylbutyn-1-yl)cycloalkan-1-ols were prepared by the action of (2-lithiooxy-2-methylbutyn-3-yl)lithium on cyclopentanone, cyclohexanone, cycloheptanone, and cyclododecanone. The products react with acetonitrile under Ritter reaction conditions. Therewith, in the presence of 8 g-equiv of sulfuric acid, a 2:1 mixture of 1-acetylamino-1-(2-acetylamino-2-methylbutyn-3-yl)cycloalkanes and 1-acetylamino-1-(3-acetylamino-3-methylbutyryl)cycloalkanes is formed, whereas in the presence of 2 g-equiv of the acid, a mixture of 1-acetylamino-1-(2-acetylamino-2-methylbutyn-3-yl)cycloalkanes and 1-acetylamino-1-(3-methyl-2-butenoyl)cycloalkanes in the same ratio.     

The reaction of photochemically generated α-hydroxyalkyl radicals with alkynes: a synthetic route to γ-butenolides

The photomediated generation of α-hydroxyalkyl radicals from simple acyclic and cyclic alcohols, and acyclic diols, and their subsequent carbon-carbon bond forming reaction with propiolate esters and acetylenedicarboxylates, gives a mixture of a β-(hydroxyalkyl)enoate, the result of a formal cis addition, and the unsaturated lactone (γ-butenolide) resulting from the spontaneous cyclization of the corresponding trans addition product. Treatment of the cis adduct with NBS converts it to the same lactone, and so the method overall constitutes a particularly direct route to this important structural unit. Cyclic alcohols give rise to spiro-γ-butenolides. The use of supported photomediators simplifies product isolation and allows for the recovery and reuse of the photomediator.     

Contingency and serendipity in the reactions of Fischer carbene complexes with conjugated triynes

The first examples of reactions of Fischer carbene complexes with triynes are reported. The regioselectivity of the reaction of the two different alkyne functions in the symmetrical triyne depends on the nature of the substituent of the triyne. Bis-silyl-substituted triynes react at the central alkyne unit, whereas bis-aryl- and bis-alkyl-substituted triynes react at the end alkyne unit. The reaction of a Fischer carbene complex with a phenyl substituent also reacts with a bis-silyl-substituted triyne at the central alkyne unit but gives a furan product rather than the normal phenol product. It was also demonstrated that all three of the alkyne units in conjugated triynes could react in turn with a Fischer carbene complex to give access to trisquinones.     

Cobalt-catalyzed intermolecular [2 + 2 + 2] cycloaddition for the synthesis of 1,3-cyclohexadienes

A cobalt(I)-catalyzed [2 + 2 + 2] cycloaddition reaction between an internal acceptor-substituted alkyne and a terminal alkene leads to the formation of regiochemically enriched polysubstituted 1,3-cyclohexadiene derivatives in acceptable yields when methyl butynoate is used, whereas regiochemically pure products are formed in good yields form phenyl propyonate. The concurrent cyclotrimerization reaction of the alkyne to the corresponding benzene derivative is dependent on the sterical bulk of the alkyne and is considerably reduced with the sterically more hindered alkyne.     

Cobalt‐Catalyzed Intermolecular [2+2] Cycloaddition between Alkynes and Allenes

An intermolecular [2+2] cycloaddition reaction between an alkyne and an allene is reported. In the presence of a cobalt(I)/diphosphine catalyst, a near equimolar mixture of the alkyne and allene is converted into a 3‐alkylidenecyclobutene derivative in good yield with high regioselectivity. The reaction tolerates a variety of internal alkynes and mono‐ or disubstituted allenes bearing various functional groups. The reaction is proposed to involve regioselective oxidative cyclization of the alkyne and allene to form a 4‐alkylidenecobaltacyclopentene intermediate, with subsequent C?C reductive elimination.     

Catalytic metallonitrene/alkyne metathesis: a powerful cascade process for the synthesis of nitrogen-containing molecules

A conceptually novel metallonitrene/alkyne metathesis cascade reaction has been developed for the construction of nitrogen-containing compounds from simple alkyne starting materials. Rhodium(II) tetracarboxylate salts are efficient catalysts for this reaction, in which an electrophilic rhodium nitrene is trapped by an alkyne, resulting in the formation of a new C-N bond and the generation of a reactive metallocarbene for cascade reaction. The reaction is tolerant of both alkyl and aryl substituents on the alkyne, and proceeds at room temperature in a variety of common solvents. The modular nature of the reaction allows for the rapid construction of congested bicyclic systems from remarkably simple alkyne starting materials.     

Preparation of 1H‐1,2,3‐Triazoles by Cuprous Ion Mediated Cycloaddition of Terminal Alkyne and Sodium Azide

1H‐1,2,3‐triazoles can be prepared in good yield by the reaction of terminal alkyne and sodium azide in the presence of cuprous chloride at a temperature higher than 70°C. The alkyne is unactivated and the reaction has to be carried out under inert gas. At room temperature, the reaction first gives a Cu(I)‐azide complex which is converted to a Cu‐alkyne complex when the temperature is raised to higher than 70°C. The reaction of Cu(I)‐alkyne complex and azide ion dissociated from or coordinated to Cu(I) then gives 1H‐1,2,3‐triazoles.     

Peroxide-mediated efficient addition of cycloalkanes to imines

A novel direct addition of cycloalkanes to imines mediated by peroxide was developed. The reaction tolerates a wide range of functionalities as well as aqueous conditions.     

Controllable glycosylation of polyphosphazene via radical thiol–yne click chemistry

We describe a versatile approach to synthesize glycosylated polyphosphazenes with controllable density of glycosyl groups. These glycopolymers have been synthesized by the nucleophilic substitution of poly(dichlorophosphazene) with propargylamine and subsequent “thiol–yne” click reaction between poly[di(propargylamine)phosphazene] and 2,3,4,6‐tetra‐O‐acetyl‐1‐thio‐β‐D ‐glucopyranose (SH‐GlcAc₄). The polymers were characterized with FTIR and ¹H NMR. We found that the high steric hindrance of SH‐GlcAc₄ plays a key role in the overall reaction process, and ～55% of the alkyne groups participate in the “thiol–yne” click reaction. About 8% of the alkyne groups convert to alkene groups at the end of click reaction. The substitution of alkyne/alkane mixture was conducted to reduce the alkyne density in the side groups of polyphosphazenes and minimize the influences of this steric effect. Mixed‐substituent polyphosphazene was synthesized with 2:3 ratio of alkyne and alkane. In this case, almost no alkyne group remains after the “thiol–yne” click reaction, and thus the glycosylated polyphosphazene is able to form into micelles through self‐assembly process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Cobalt-mediated two-carbon ring expansion of five-membered rings. Electrophilic carbon-carbon bond activation in the synthesis of seven-membered rings

Electrophilic cobalt(III) mediates an unprecedented two-carbon ring expansion of coordinated five-membered rings, leading to a remarkably general new strategy for the synthesis of seven-membered carbocycles from readily available five-membered ring substrates. The reaction, a metal-mediated [5 + 2] cyclopentenyl/alkyne cycloaddition, proceeds via initial protonation of a cobalt(I) cyclopentadiene complex, followed by rearrangement to an agostic eta3-cyclopentenyl intermediate. The cyclic eta3-allyl residue then undergoes migratory coupling with alkyne followed by carbon-carbon bond activation of the unstrained five-membered ring and recyclization to the ring expanded product, although the order of events and intimate mechanism has not been conclusively established. The reaction is highly selective with respect to which five-membered ring ligand undergoes activation, presumably a consequence of rapid cobalt-mediated interannular hydride transfer and kinetic preference for alkyne insertion into the less substituted cyclopentenyl ring. The alkyne insertion is itself highly regioselective, proceeding via migration to the sterically smaller end of the alkyne. The reaction is sensitive to both the cobalt counterion and the ancillary eta5-cyclopentadienyl substituent but proceeds for a considerable range of alkyl-, aryl-, and trialkylsilyl-substituted terminal and internal alkynes.     

Direct synthesis of highly pure perylene tetracarboxylic monoimide

A series of perylene tetracarboxylic monoimides substituted with cycloalkanes were synthesized through a one-step reaction between cycloalkyl amines and the parent perylene dianhydride. The reaction demonstrates high selectivity for the production of monoimides with no formation of diimides. The high reaction selectivity is primarily due to the insolubility of the monoimides in the reaction medium, which in turn causes rapid precipitation of the products, shifting the reaction equilibrium to the right.     

Frustrated Lewis Pair Mediated 1,2-Hydrocarbation of Alkynes

Frustrated Lewis pair (FLP) chemistry enables a rare example of alkyne 1,2-hydrocarbation with N-methylacridinium salts as the carbon Lewis acid. This 1,2-hydrocarbation process does not proceed through a concerted mechanism as in alkyne syn-hydroboration, or through an intramolecular 1,3-hydride migration as operates in the only other reported alkyne 1,2-hydrocarbation reaction. Instead, in this study, alkyne 1,2-hydrocarbation proceeds by a novel mechanism involving alkyne dehydrocarbation with a carbon Lewis acid based FLP to form the new C−C bond. Subsequently, intermolecular hydride transfer occurs, with the Lewis acid component of the FLP acting as a hydride shuttle that enables alkyne 1,2-hydrocarbation.     

O‐Alkyl S‐3,3‐Dimethyl‐2‐oxobutyl Dithiocarbonates as Versatile Sulfur‐Transfer Agents in Radical C(sp3)?H Functionalization

Boiling of the title compounds in ethereal solvents or cycloalkanes in the presence of a radical initiator leads to radical C(sp³)? H functionalization, by which a sulfur atom is introduced into the ethereal solvents at the oxygenated carbon atom or into the cycloalkanes. Both acyclic and cyclic ethers, such as [18]crown‐6 and [D₈]THF, undergo the sulfur transfer. The reaction is useful for the synthesis of monothioacetals, thiols, and sulfides from simple starting materials.     

Synthesis of 1,2-bis(methoxyamino)cycloalkanes from alicyclic 1,2-bis(hydroxyamines)

Derivatives of 1,4-dihydroxypiperazine-2,3-dione were obtained by reaction of cis-1,2-bis(hydroxyamino)cycloalkanes with diethyl oxalate. Their alkylation with CH₂N₂ or Mel afforded 1,4-dimethoxypiperazine-2,3-diones. Hydrolysis of the latter gave 1,2-bis(methoxyamino)cycloalkanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 925–929, April, 1996.     

Hydrotris(3-mesitylpyrazolyl)borato-copper(I) alkyne complexes: synthesis, structural characterization and rationalization of their activities as alkyne cyclopropenation catalysts

The use of the bulky hydrotris(3-mesitylpyrazolyl)borate anionic ligand has allowed the synthesis of stable Tp(Ms)Cu(alkyne) complexes (alkyne = 1-hexyne, 1, phenylacetylene, 2, and ethyl propiolate, 3). The spectroscopic and structural features of these compounds and their relative reactivity have been examined, indicating the existence of a low π back-bonding from the copper(I) centre to the alkyne. Ligand exchange experiments have shown that terminal alkyne adducts are more stable than internal alkyne analogues. In good accordance with this, the previously reported alkyne cyclopropenation reaction catalysed by the Tp(x)Cu complexes can be rationalized and correlated with their relative stability.     

One‐Pot Synthesis of Lactams from Cycloalkanes and tert‐Butyl Nitrite by Using N‐Hydroxyphthalimide as Key Catalyst

Lactams were successfully synthesized in the one‐pot reaction of cycloalkanes and tBuONO in the presence of N‐hydroxyphthalimide as a key catalyst. Cyclododecane and cyclohexane were treated with tBuONO followed by triethylamine and then cyanuric chloride in a one‐pot manner to give laurolactam and ε‐caprolactam, respectively, in good yields. The Beckmann rearrangement of oximes by cyanuric chloride was found to be accelerated by the use of 1,1,1,3,3,3‐hexafluoro‐2‐propanol as solvent. The method provides the first successful environmentally benign direct synthetic route to lactams from cycloalkanes without the formation of any salt.     

Theoretical study of the reaction mechanisms involved in the thermal intramolecular reactions of 1,6-fullerenynes

Substitution of a H atom by an alkyl group on the terminal carbon of the alkyne moiety of 1,6-fullerenynes has a strong impact on the products of the reaction undergone by this species after thermal treatment. While the reaction of 1,6-fullerenynes bearing an unsubstituted alkyne moiety results in the cycloaddition of the alkyne group to the fullerene double bond leading to cyclobutene-fused derivatives, the presence of an alkyl substituent leads to the formation of allenes. In the present work, we have performed an exhaustive theoretical analysis of all possible reaction mechanisms leading to cyclobutene-fused derivatives and allenes to offer an explanation of the reactivity differences observed. The results obtained show that formation of cyclobutene-fused derivatives occurs through a stepwise diradical reaction mechanism, while allene formation proceeds through a concerted way involving an uncommon intramolecular ene process. For the 1,6-fullerenynes bearing a substituted alkyne, the ene reaction path leading to allenes has an energy barrier somewhat lower than the stepwise diradical mechanism for the cyclobutene-fused derivative formation, thus explaining the outcome of the reaction.     

Competition between C-C and C-H Activation in Reactions of Neutral Nickel Atom with Cycloalkanes （n = 3-7）

A theoretical investigation of the reaction mechanisms for C-H and C-C bond activation processes in the reaction of Ni with cycloalkanes C,,H2. （n = 3-7） is carried out. For the Ni ＋ CnH2, （n = 3, 4） reactions, the major and minor reaction channels involve C-C and C-H bond activations, respectively, whereas Ni atom prefers the attacking of C-H bond over the C-C bond in CnH2n （n = 5=7）. The results are in good agreement with the experimental study. In all cases, intermediates and transition states along the reaction paths of interest are characterized, It is found that both the C-H and C-C bond activation processes are proposed to proceed in a one-step manner via one transition state. The overall C-H and C-C bond activation processes are exothermic and involve low energy barriers, thus transition metal atom Ni is a good mediator for the activity of cycloalkanes CnH2n （n = 3 -7）.     

Sm-Catalyzed Synthesis and Biological Activity of Acyclic and Cyclic Azadiperoxides

Russian Journal of Organic Chemistry - Acyclic diaminodiperoxides and cyclic azadiperoxides are synthesized by the reaction of 1,1-bis-(hydroperoxy)cycloalkanes with formaldehyde and primary...