Big Chemical Encyclopedia

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

Articles Figures Tables About

Thiocarbonyl ylides 1,3-dipolar cycloadditions

When thiocarbonyl derivatives are treated with an excess of electrophilic carbene complex, alkenes are usually obtained [1333-1336], The reaction is believed to proceed by the mechanism sketched in Figure 4.18, closely related to the thiocarbonyl olefination reaction developed by Eschenmoser [1337], Few examples have been reported in which stable thiiranes could be isolated [1338], The intermediate thiocarbonyl ylides can also undergo reactions similar to those of carhonyl ylides, e.g. 1,3-dipolar cycloadditions or 1,3-oxathiole formation [1338], Illustrative examples of these reactions are given in Table 4.22. [Pg.216]

When planning reactions of thiocarbonyl compounds with electrophilic carbene complexes it should be taken into aceount that thiocarbonyl compounds can undergo uncatalyzed 1,3-dipolar cycloaddition with acceptor-substituted diazomethanes to yield 1,3,4-thiadiazoles. These can either be stable or eliminate nitrogen to yield thiiranes or other products similar to those resulting from thiocarbonyl ylides [1338]. [Pg.216]

Like other 1,3-dipolar species, thiocarbonyl ylides are able to enter intramolecular as well as intermolecular cycloaddition reactions. In this chapter, selected examples of both types will be illustrated. [Pg.324]

Karlsson and Hogberg (291,292) applied the thiocarbonyl ylide 175 in a diastereoselective 1,3-dipolar cycloaddition with 165. The thiocarbonyl yhde was generated in situ by an elimination reaction. The reaction with 165 gave 176 (R = Bu, BnO, Ph) with selectivities of up to 64—80% de. Furthermore, the cycloaddition of a chiral galactose-derived nitrile imine with 165 has been reported (104). [Pg.855]

Most nonclassical condensed thiophenes that have been prepared, (53) being an exception, are quite reactive and undergo reactions characteristic of 1,3-dipolar intermediates. The 1,3-dipole need not, however, be a thiocarbonyl ylide (55) has been generated and it undergoes cycloadditions as a carbonyl ylide, this being the 1,3-dipolar form illustrated (72JA6214, 74JA1817). [Pg.723]

Organosilicon compounds have also been reacted with thiocarbonyl ylides to afford a variety of heterocycles468,469 and in Section III.F.5 we pointed out the 1,3-dipolar cycloaddition between in situ generated thioaldehydes and a pyrazolidinium ylide to produce a nuclear analogue of pyrazolidinone antibacterial agents332. Moreover, Vedejs has applied the dipolar cycloaddition between a thione, generated from a Norrish-type II fragmenta-... [Pg.1449]

The 1,3-dipolar cycloaddition of the carbonyl ylide (31) to the aldimine (32) produces the adduct (33), which has been used to synthesize the taxol C(13) side-chain (34), which is known to be required for the antitumour activity of taxol (Scheme 9).35 The dirhodium tetraacetate-catalysed decomposition of l-diazo-5-phenylpentane-2,5-dione (35) yields the carbonyl ylide (36), which cycloadds to methylenecyclopropanes (37) to produce spirocyclopropanated 8-oxabicyclo[3.2.1]octan-2-ones [(38)-(40)] in 6-75% yields (Scheme 10).36 The 1,3-dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides with thiobenzophenone produce both regioisomeric 1,3-dithiolanes as expected. However, in the case of highly sterically hindered thiocarbonyl ylides, methylene transfer leads to the formation of 4,4,5,5-tetraphenyl-l,3-dithiolane.37,38... [Pg.355]


See other pages where Thiocarbonyl ylides 1,3-dipolar cycloadditions is mentioned: [Pg.2]    [Pg.327]    [Pg.345]    [Pg.348]    [Pg.354]    [Pg.610]    [Pg.70]    [Pg.12]    [Pg.251]    [Pg.269]    [Pg.272]    [Pg.278]    [Pg.590]    [Pg.722]    [Pg.1060]    [Pg.1075]    [Pg.1093]    [Pg.1446]    [Pg.359]   
See also in sourсe #XX -- [ Pg.1074 , Pg.1093 , Pg.1094 ]

See also in sourсe #XX -- [ Pg.4 ]

See also in sourсe #XX -- [ Pg.4 ]




SEARCH



Thiocarbonyl

Thiocarbonyl ylide

Thiocarbonyl ylides

Thiocarbonyl ylides 3 + 2] cycloadditions

Thiocarbonyl ylides, 1,3-dipolar cycloaddition

Thiocarbonylation

Thiocarbonyls

Ylides cycloaddition

© 2024 chempedia.info