Bond Migration Research Articles

Recent applications of the 1,2-carbon atom migration strategy in complex natural product total synthesis.

1,2-Carbon atom rearrangement has been broadly applied as a guiding strategy in complex molecule assembly. As it entails the carbon-carbon or carbon-heteroatom bond migration between two vicinal atoms, this type of reaction is capable of generating structural complexity through a molecular skeletal reorganization. This review will focus on recent employment of this strategy in the total synthesis of natural products, highlighting the exceptional utility of such synthetic methodologies in the construction of intricate carbocycles, heterocycles or structurally complex motifs from synthetically more accessible precursors.

A novel preparation of chlorophospholenium chlorides and their application in the synthesis of phospholene boranes

A novel preparation of 1-chloro-3-methyl-3-phospholenium chlorides was developed by reacting 1-substituted-3-methyl-3-phospholene 1-oxides with oxalyl chloride. The obtained cyclic chlorophosphonium salts were reacted with LiBH4 to afford the corresponding 1-substituted-3-methyl-3-phospholene boranes. The latter protocol involves a silane-free deoxygenation, and borane complex formation. In one instance, a 2-phospholene borane and the corresponding P-oxide were synthesized via rearrangement of the double bond in the cyclic chlorophosphonium salt. This double bond migration was investigated by quantum chemical calculations.

Regioselective Synthesis of Pyrroles from Alkyne‐Isocyanide Click Reactions: An Angle Strain‐Induced Bond Migration Approach

AbstractThe direct regioselective synthesis of highly functionalized pyrroles with two different electron‐withdrawing groups has been developed using an angle strain‐induced 1,2‐shift of an electron‐withdrawing group in 2H‐pyrroles. The preferential migration aptitude of an electron‐withdrawing group over alkyl and aryl groups is believed to be the result of the orbital overlap between the internal alkene and the electron‐withdrawing group. The newly developed regioselective synthesis of pyrroles features a wide substrate scope, simple reaction set‐up, and high yields (60–82%), capturing the essence of alkyne‐isocyanide “click” reactions.magnified image

Structural Determination, DFT Calculation, and Formation Mechanism of Ethyl 2-Cyano-3-alkoxypent-2-enoates Synthesized via Ru-Mediated Coupling Reaction between α,β-Unsaturated Acetals and Cyanoacetate

Abstract Ethyl 2-cyano-3-alkoxypent-2-enoates were synthesized in moderate yields via the coupling reaction between α,β-unsaturated acetals and cyanoacetate, catalyzed by [RuHCl(CO)(PPh3)3]. The E- and Z-isomers were separated and determined by X-ray crystallography for the first time. Structural distortion associated with steric hindrance around the tetrasubstituted alkene moiety was revealed: e.g., the C(carbonyl)–C(α)–C(β) angle expands to about 125°. Density functional theory calculation was performed, and the restricted B3LYP hybrid functional with the 6-31G(d,p) basis set was found to successfully elucidate the solid-state structure and conformation, as well as spectroscopic properties. A plausible formation mechanism was proposed, in which the Ru complex catalyzed the C=C bond migration of the α,β-unsaturated acetal to give the corresponding ketene acetal and assisted the subsequent condensation reaction with cyanoacetate to some extent.

Reaction pathway mechanism of thermally induced isomerization of 9,12-linoleic acid triacylglycerol.

To clarify the formation mechanism of trans linoleic acid isomers in edible oils during the heating process, trilinolein and trilinoelaidin, as representative oils, were placed in glass ampoules and sealed before heating at 180, 240 and 320 °C. The glass ampoules were removed at regular time intervals, and the contents were analyzed by infrared spectroscopy. The samples were then subjected to derivatization into their methyl esters for gas chromatographic analysis. Analysis results show that 9c,12c and 9t,12t fatty acids from trilinolein and trilinoelaidin molecules undergo chemical bond rotation, migration and degradation, leading to the formation of non-conjugated linoleic acids (NLAs), conjugated linoleic acids (CLAs) and aldehydes. The formation rate of isomers from the 9c,12c fatty acid is higher than that of the 9t,12t fatty acid. The production of aldehydes increases with heating temperature and time. The isomerization pathways involved in the formation of NLAs and CLAs during heating are clearly presented. These findings suggest possible pathways of NFA and CFA formation from heated trilinolein and trilinoelaidin, complement the mechanistic studies previously published in the literature, and provide a theoretical basis for future control of the quality and safety of fats and oils. © 2016 Society of Chemical Industry.

Genome-Based Discovery of an Unprecedented Cyclization Mode in Fungal Sesterterpenoid Biosynthesis.

Sesterterpenoids are a group of terpenoid natural products that are primarily biosynthesized via cyclization of the C25 linear substrate geranylfarnesyl pyrophosphate (GFPP). Although the long carbon chain of GFPP in theory allows for many different cyclization patterns, sesterterpenoids are relatively rare species among terpenoids, suggesting that many intriguing sesterterpenoid scaffolds have been overlooked. Meanwhile, the recent identification of the first sesterterpene synthase has allowed the discovery of new sesterterpenoids by the genome mining approach. In this study, we characterized the unusual fungal sesterterpene synthase EvQS and successfully obtained the sesterterpene quiannulatene (1) with a novel and unique highly congested carbon skeleton, which is further oxidized to quiannulatic acid (2) by the cytochrome P450 Qnn-P450. A mechanistic study of its cyclization from GFPP indicated that the biosynthesis employs an unprecedented cyclization mode, which involves three rounds of hydride shifts and two successive C-C bond migrations to construct the 5-6-5-5-5 fused ring system of 1.

Benzannulation of Triynes Initiated by an Alder-Ene Reaction and Subsequent Trifluoromethylthiolate Addition

A new benzannulation reaction with accompanied trifluoromethylthiolation is described. This benzannulation can generate a range of trifluoromethylthiolated benzolactams and benzolactones from 1,3,8-triynes and a stoichiometric amount of AgSCF3 at 90 °C through an initial Alder-ene reaction, 1,4-addition of AgSCF3, and a series of bond-reorganization processes that include double bond migration, 6π-electrocyclization, and a [1,3]-H shift. For certain substrates containing a triisopropylsilyl (TIPS) group, the final [1,3]-H shift-interrupted products, were obtained.

Co(III)-Catalyzed, Internal and Terminal Alkyne-Compatible Synthesis of Indoles

A Co(III)-catalyzed, internal and terminal alkyne-compatible indole synthesis protocol is reported herein. The N-amino (hydrazine) group imparts distinct, diverse reactivity patterns for directed C-H functionalization/cyclization reactions. Notable synthetic features include regioselectivity for a meta-substituted arylhydrazine, regioselectivity for a chain-branched terminal alkyne, formal incorporation of an acetylenic unit through C2-desilylation on a C2-silylated indole derivative, formal inversion of regioselectivity through consecutive C3-derivatization and C2-desilylation processes, and formal bond migration for a linear-chain terminal alkyne.

Colochiroside E, an Unusual Non-holostane Triterpene Sulfated Trioside from the Sea Cucumber Colochirus Robustus and Evidence of the Impossibility of a 7(8)-Double Bond Migration in Lanostane Derivatives having an 18(16)-Lactone

The unusual non-holostane triterpene glycoside, colochiroside E (1) was isolated from the sea cucumber Colochirus robustus (Cucumariidae, Dendrochirotida). The structure of 1 was established by analysis of 1D, 2D NMR and HRESI MS data. Colochiroside E (1) belongs to a rare group of glycosylated 9β-H-lanosta-18(16)-lactones and has an unprecedented sulfated trisaccharide carbohydrate chain consisting of two glucose and one xylose units. In contrast with (9β-H)-7(8)-unsaturated holostane glycosides, the 7(8)-double bond in the having (9β-H)-configuration aglycone of colochiroside E is not capable of migration into the 8(9)- and then into the 9(11)-position on treatment with HCl. The formation of a chlorine derivative of 1 was observed under these conditions.

Total synthesis of dysidavarone A

Dysidavarone A is a sesquiterpene isolated from the South China Sea sponge Dysidea avara and was reported that it showed significant anticancer activities. Because the compound has unique ‘dysidavarane’ carbon skeleton and potent biological activity, a seven-step stereoselective synthesis of dysidavarone A was developed. The key steps of the synthesis involved stereoselective reductive-alkylation, intramolecular α-arylation and double bond migration reaction. The anti-proliferation activities of Dysidavarone A against human kidney carcinoma cell lines 786-O and human prostate cancer cell lines PC-3 were also assessed.

DFT Rationalization of the Diverse Outcomes of the Iodine(III)-Mediated Oxidative Amination of Alkenes.

A computational study of the mechanism for the iodine(III)-mediated oxidative amination of alkenes explains the experimentally observed substrate dependence on product distribution. Calculations with the M06 functional have been carried out on the reaction between PhI(N(SO2 Me)2 )2 and three different representative substrates: styrene, α-methylstyrene, and (E)-methylstilbene. All reactions start with electrophilic attack by a cationic PhI(N(SO2 Me)2 )(+) unit on the double bond, and formation of an intermediate with a single C-I bond and a planar sp(2) carbocationic center. The major path, leading to 1,2-diamination, proceeds through a mechanism in which the bissulfonimide initially adds to the alkene through an oxygen atom of one sulfonyl group. This behavior is now corroborated by experimental evidence. An alternative path, leading to an allylic amination product, takes place through deprotonation at an allylic C-H position in the common intermediate. The regioselectivity of this amination depends on the availability of the resonant structures of an alternate carbocationic intermediate. Only in cases where a high electronic delocalization is possible, as in (E)-methylstilbene, does the allylic amination occur without migration of the double bond.

SYNTHETIC TRANSFORMATIONS OF SESQUITERPENE LACTONES. 9. SYNTHESIS OF 13-(PYRIDINYL)EUDESMANOLIDES

The reaction of isoalantolactone, a sesquiterpene α-methylidene-γ-lactone, with bromo(iodo)pyridines under the Heck reaction conditions gave 3-(pyridylmethylidene)-8а-methyldecahydronaphtho[2,3- b ]furan-2(3 Н )-ones and 3-(pyridylmethyl)-8а-methyloctahydronaphtho[2,3- b ]furan-2(4 Н )-ones, products of double bond migration. The yield and product ratio depended on the reaction conditions and the nature of halopyridine. The effectiveness of Pd(OAc) 2 –caffeine catalytic system was demonstrated in this reaction. How to Cite Patrushev, S. S.; Shakirov, M. M.; Shults, E. E. Chem. Heterocycl. Compd. 2016 , 52 , 165. [ Khim. Geterotsikl. Soedin. 2016 , 52 , 165.] For this article in the English edition see DOI 10.1007/s10593-016-1855-1

Raman and nuclear magnetic resonance investigation of alkali metal vapor interaction with alkene-based anti-relaxation coating.

The use of anti-relaxation coatings in alkali vapor cells yields substantial performance improvements compared to a bare glass surface by reducing the probability of spin relaxation in wall collisions by several orders of magnitude. Some of the most effective anti-relaxation coating materials are alpha-olefins, which (as in the case of more traditional paraffin coatings) must undergo a curing period after cell manufacturing in order to achieve the desired behavior. Until now, however, it has been unclear what physicochemical processes occur during cell curing, and how they may affect relevant cell properties. We present the results of nondestructive Raman-spectroscopy and magnetic-resonance investigations of the influence of alkali metal vapor (Cs or K) on an alpha-olefin, 1-nonadecene coating the inner surface of a glass cell. It was found that during the curing process, the alkali metal catalyzes migration of the carbon-carbon double bond, yielding a mixture of cis- and trans-2-nonadecene.

Synthetic transformations of sesquiterpene lactones 9.* Synthesis of 13-(pyridinyl)eudesmanolides

The reaction of isoalantolactone, a sesquiterpene α-methylidene-γ-lactone, with bromo(iodo)pyridines under the Heck reaction conditions gave 3-(pyridylmethylidene)-8а-methyldecahydronaphtho[2,3-b]furan-2(3Н)-ones and 3-(pyridylmethyl)-8а-methyloctahydronaphtho[2,3-b]-furan-2(4Н)-ones, products of double bond migration. The yield and product ratio depended on the reaction conditions and the nature of halopyridine. The effectiveness of Pd(OAc)2–caffeine catalytic system was demonstrated in this reaction.

C-C Bond Migration in the Cycloisomerization of 1,6-Enynes.

A full account of our investigation of C-C bond migration in the cycloisomerization of oxygen-tethered 1,6-enynes is described. Under Pt(II) and/or Ir(I) catalysis, cyclic and acylic alkyl groups were found to undergo 1,2-shifts into metal carbenoid intermediates. Interestingly, this process does not appear to be driven by the release of ring strain, and thus provides access to large carbocyclic frameworks. The beneficial effect of CO on the Pt(II) and Ir(I) catalytic systems is also evaluated.

Titanium and Zirconium Hydride-Catalyzed Regioselective Isomerization of 1,4-Dihydrofulvenes: Access to 1-Substituted 1,2-Dihydrofulvenes.

Zirconium hydride-catalyzed C═C double bond migration from nonconjugated to conjugated dienes is described. Applied to 1-substituted 1,4-dihydrofulvenes, the migration leads selectively to 1-substituted 1,2-dihydrofulvenes. The C═C double bond migration can also be catalyzed by titanium hydride, allowing a one-pot procedure to provide 1-substituted 1,2-dihydrofulvenes from pentafulvenes via two titanium-catalyzed steps. This sequence was proven to be temperature-dependent, allowing the selective access to a conjugated or nonconjugated adduct by a simple temperature tuning. The synthetic potential of the methodology was illustrated by the diastereoselective synthesis of a polyhydroxycyclopentane.

ChemInform Abstract: Synthesis of Polysubstituted γ‐Butenolides via a Radical Pathway: Cyclization of α‐Bromo Aluminium Acetals and Comparison with the Cyclization of α‐Bromoesters at High Temperature.

AbstractA four‐step one‐pot procedure involving generation of α‐bromo aluminum acetals, their subsequent radical cyclization followed by oxidation of the resulting cyclic aluminum acetals and base promoted double bond migration is developed to convert α‐bromoesters derived from propargylic alcohols to butenolides.

Gold-Catalyzed Ring Expansion of Alkynyl Heterocycles through 1,2-Migration of an Endocyclic Carbon-Heteroatom Bond.

A mild and efficient gold-catalyzed oxidative ring-expansion of a series of alkynyl heterocycles using pyridine-N-oxide as the oxidant has been developed, which affords highly valuable six- or seven-membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon-heteroatom bond (favored over C-H migration) with the order of migratory aptitude for carbon-heteroatom bonds being C-S>C-N>C-O. In the absence of an oxidant, polycyclic products are readily constructed through a ring-expansion/Nazarov cyclization reaction sequence.

Complete H–D Exchange of Butene via D Absorbed in a Pd–Au Alloy

The H–D exchange reaction is one of the easiest ways to synthesize deuterium-labeled compounds. H–D exchange of olefins has been widely studied on metal surfaces such as Pd and Pt. However, H–D exchange of butene on these surfaces is hardly completed and always accompanied by hydrogenation or dehydrogenation, and its reaction mechanism is yet to be elucidated. In the present study, we investigated the reaction of cis-2- and 1-butenes with H and D atoms absorbed in the near-surface region of Pd70Au30(110) by using thermal desorption spectroscopy (TDS), reflection–absorption infrared spectroscopy (RAIRS), and TDS simulation. We show complete H–D exchange of both butene isomers without hydrogenation and dehydrogenation. Similar product yield distributions for both butene isomers indicate a fast di-σ bond migration on this surface, which is a key for the complete H–D exchange. Our results would lead to understanding and controlling the catalytic activity and selectivity of the Pd–Au alloy and Pd-related surfaces and would open up a new chemistry using absorbed hydrogen in combination with alloyed surfaces.

ChemInform Abstract: Enantioselective Construction of 3‐Hydroxypiperidine Scaffolds by Sequential Action of Light and Rhodium upon N‐Allylglyoxylamides.

3-Hydroxypiperidine scaffolds were enantioselectively constructed in an atom-economical way by sequential action of light and rhodium upon N-allylglyoxylamides. In a formal sense, the allylic CH bond was selectively cleaved and enantioselectively added across the ketonic carbonyl group with migration of the double bond (carbonyl-ene-type reaction).