Tandem Metathesis Reactions Research Articles

Simple access to alkoxysilyl telechelic polyolefins from ruthenium-catalyzed cross-metathesis depolymerization of polydienes

The first functional cross-metathesis (CM) depolymerization of commercial (co)polydienes using a ruthenium catalyst and an acyclic bis(trialkoxysilyl) difunctionalized chain-transfer agent (CTA), [(EtO)3Si(CH2)3NHC(O)OCH2CH]2 (1), towards the synthesis of low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic (co)polydienes is reported. The reactivity of three commercial grades of liquid (co)polydienes (P1–P3, polybutadienes (PBDs) or poly(butadiene-co-isoprene) (P(BD-co-IP))) differing in their end-functionalization, in the amount of 1,2-vinyl and in their dispersity, was explored. Operating conditions for effective production of α,ω-bis(trialkoxysilyl) telechelic PBDs or P(BD-co-IP)s with high chemoselectivity (80–90wt%) and catalytic productivity (non-optimized TON up to 24000) were established. The chemoselectivity of this tandem metathesis reaction was assessed in particular through detailed 2D NMR analyses. An original approach combining the CM depolymerization of PBD with the ring-opening functional metathesis polymerization (ROMP) of a cycloolefin in the presence of CTA 1has also been next implemented affording low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic copolydienes. The viscosity of the (co)polyolefins was investigated by rheological analyses.

Ring Rearrangement Metathesis in 7-Oxabicyclo[2.2.1]heptene (7-Oxanorbornene) Derivatives. Some Applications in Natural Product Chemistry

Metathesis reactions is firmly established as a valuable synthetic tool in organic chemistry, clearly comparable with the venerable Diels-Alder and Wittig reactions and, more recently, with the metal-catalyzed cross-coupling reactions. Metathesis reactions can be considered as a fascinating synthetic methodology, allowing different variants regarding substrate (alkene and alkyne metathesis) and type of metathetical reactions. On the other hand, tandem metathesis reactions such.Ring Rearrangement Metathesis (RRM) and the coupling of metathesis reaction with other reactions of alkenes such as Diels-Alder or Heck reactions,.makes metathesis one of the most powerful and reliable synthetic procedure. In particular, Ring-Rearrangement Metathesis (RRM) refers to the combination of several metathesis transformations into a domino process such as ring- opening metathesis (ROM)/ring-closing metathesis (RCM) and ROM-cross metathesis (CM) in a one-pot operation. RRM delivers complex frameworks that are difficult to assemble by conventional methods constitutingan atom economic process. RRM is applicable to mono- and polycyclie systems of varying ring sizes such as cyclopropene, cyclobutene, cyclopentene, cyclohexene, pyran systems, bicyclo[2.2.1]heptene derivatives, bicyclo[2.2.2]octene derivatives, bicyclo[3.2.l]octene derivatives and bicyclo[3.2.1]octene derivatives. In this review our attention has focused on the RRM reactions in 7-oxabicyclo[2.2.I]heptene derivatives and on their application in the synthesis of natural products or significant subunits of them.

ChemInform Abstract: Diastereoselective Synthesis of Highly Substituted Polycyclic Scaffolds via a One‐Pot Four‐Step Tandem Catalytic Process.

AbstractA one‐pot four‐step multi‐reaction process involving a thermal Overman rearrangement, a tandem metathesis reaction, and a Diels—Alder reaction is developed for the diastereoselective synthesis of aminobicyclononanes and ‐decanes with up to five stereogenic centers.

Total Synthesis of Aburatubolactam A

Total Synthesis of Aburatubolactam A

Total Synthesis of (+)-Lepadin B: Stereoselective Synthesis of Nonracemic Polysubstituted Hydroquinolines Using an RC-ROM Process

This communication describes a new tandem metathesis reaction for which an RC-ROM mechanism was experimentally supported. This process was successfully applied to the synthesis of cis-fused polyhydroquinolines enabling a short stereoselective total synthesis of ent-lepadin B.

The use of d-mannitol-derived C2-symmetric trienes in tandem metathesis reactions towards valuable lactones

Chiral lactones were synthesized from d-mannitol. C 2-symmetric triene precursors were constructed with a central relay-olefin allowing the key domino ring-closing metathesis to be achieved. It led to the symmetrical cleavage of the substrate and to the formation of 2 mol of the desired 5- or 6-membered lactone. Attempts to form 7-membered lactones thus far only led to 14-membered macrodiolides instead.

Practical Syntheses of Enantiomerically Pure N‐Acetylbenzhydrylamines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis of N-heterocyclic compounds via ene–yne metathesis reactions

Propargylamino and allylamino derivatives of cyclohexene and norbornene were subjected to tandem metathesis reactions with first and second generation Grubbs' catalysts 1 and 2. Results show that the method is compatible with suitably protected nitrogen-containing compounds. Cyclohexenes gave intriguing results in terms of the possibility to perform ring rearrangement metathesis (RRM) reactions, showing a difference with the analogous allyl and propargyl ether substrates.

Novel Development of Metathesis Reaction Using Metal Carbene Complexes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Total Synthesis of (+)-Cyanthiwigin U

A concise total synthesis of the tricyclic terpene cyanthiwigin U has been accomplished in 12 steps and 17% overall yield. The key step of the synthesis is a two-directional tandem metathesis reaction that forms the cyclohepta[e]indene core from a readily available bicyclo[2.2.2]octene.

メタルカルベン錯体を用いたメタセシス反応の新展開

Since Schrock and Grubbs discovered the molybdenum and ruthenium-carbene complexes in 1990 and 1992, metathesis reactions have been a useful tool in synthetic organic chemistry. As the metathesis reaction, olefin metathesis, enyne metathesis and alkyne metathesis are known. The carbon-carbon double or triple bonds are cleaved and the double or triple bonds are formed simultaneously in the metathesis reaction. Novel synthetic methods for the carbo- and hetero-cyclic compounds from diene, enyne and diyne have been developed using these reactions. The tandem metathesis reactions were also developed and many bond cleavages and bond formations occurred in one step reaction to form various functionalized compounds. For development of asymmetric metathesis reaction, novel molybdenum- and ruthenium-catalysts were also synthesized and asymmetric ring-opening and ring-closing metatheses were carried out to form optically active compounds with the high ee. The novel syntheses of the natural products and the biologically active substances have been achieved using these reactions.

Unusual Macrocyclic Spirocycles from Tandem Metathesis Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Unusual macrocyclic spirocycles from tandem metathesis reactions

This letter details the formation of 18-membered macrocyclic spirocyclic esters and ethers from readily prepared tetraene precursors via tandem metathesis reactions. Factors which control the course of these transition metal catalysed processes are discussed and the crystal structures of the novel macrocycles obtained are delineated.

Totally atom economical tandem-metathesis and Diels–Alder approach to polycyclic compounds

Norbornene derivatives bearing pendant alkynes undergo a series of tandem metathesis reactions when treated with Grubbs’ catalyst. The products of this cascade are dienes which can be trapped in situ by dienophiles in Diels–Alder reactions to yield polycyclic compounds.

Variable and stereoselective synthesis of azasugar analogues by a ruthenium-catalyzed ring rearrangement

A novel ruthenium-catalyzed ring opening/ring closing tandem metathesis reaction with a catalytic transfer of stereocenters from a ring to an olefinic chain is described. This ring rearrangement serves as the key step in the stereoselective synthesis of the new azasugar analogues 1 and 2.