Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Ring structures five-membered rings

Intramolecular insertion reactions present new synthetic solutions. Generally, rigid structures favor such insertions. When an intramolecular insertion is possible, no intermolecular insertions are seen. In flexible structures, five-membered ring formation is preferred to six-membered ring formation. Both inter- and intramolecular insertions are amendable to asymmetric induction by choosing chiral ligands on metal centers. Arylcarbene can be inserted intramolecularly into aromatic C-H bonds (Schemes 5.49 and 5.50). [Pg.180]

In the alkylative cyclization of the 1,6-enyne 372 with vinyl bromide, formation of both the five-membered ring 373 by exn mode carbopalladation and isomerization of the double bonds and the six-membered ring 374 by endo mode carbopalladation are observed[269]. Their ratio depends on the catalytic species. Also, the cyclization of the 1,6-enyne 375 with /i-bromostyrene (376) affords the endo product 377. The exo mode cyclization is commonly observed in many cases, and there are two possible mechanistic explanations for that observed in these examples. One is direct endo mode carbopalladation. The other is the exo mode carbopalladation to give 378 followed by cyclopropana-tion to form 379, and the subsequent cyclopropylcarbinyl-homoallyl rearrangement affords the six-membered ring 380. Careful determination of the E or Z structure of the double bond in the cyclized product 380 is crucial for the mechanistic discussion. [Pg.180]

A compound (CgHjo) contains a five membered ring When Bt2 adds to it two diaste reomenc dibromides are formed Suggest reasonable structures for the compound and the two dibromides... [Pg.325]

Firefly lucifenn is an example of an azole that contains a benzene ring fused to the five membered ring Such structures are fairly common Another example is benzimidazole present as a structural unit m vitamin B12 Some compounds related to benzimidazole include purine and its ammo substituted derivative adenine one of the so called het erocychc bases found m DNA and RNA (Chapter 28)... [Pg.461]

This polymerization is carried out in the two stages indicated above precisely because of the insolubility and infusibility of the final product. The first-stage polyamide, structure [IX], is prepared in polar solvents and at relatively low temperatures, say, 70°C or less. The intermediate is then introduced to the intended application-for example, a coating or lamination-then the second-stage cyclization is carried out at temperatures in the range 150-300°C. Note the formation of five-membered rings in the formation of the polyimide, structure [X], and also that the proportion of acid to amine groups is 2 1 for reaction (5.II). [Pg.335]

Structure of Five-membered Rings with One Heteroatom... [Pg.2]


See other pages where Ring structures five-membered rings is mentioned: [Pg.728]    [Pg.155]    [Pg.632]    [Pg.756]    [Pg.102]    [Pg.107]    [Pg.102]    [Pg.325]    [Pg.515]    [Pg.335]    [Pg.459]    [Pg.94]    [Pg.436]   


SEARCH



14-membered ring structures

Alkenes derivatives, five-membered ring structure

Five-membered ring

Five-membered ring structures, -coordination

Heteroaromatic compounds five-membered aromatic ring structures

Olefins derivatives, five-membered ring structure

Ring compounds, structure five-membered

Ring structures

Ring structures 5- membered rings

Structure comprising Two Five-Membered Rings

Structure of Five-membered Rings with One Heteroatom

Structure of Five-membered Rings with Two or More Heteroatoms

Thiophene derivatives five-membered ring structure

© 2024 chempedia.info