Big Chemical Encyclopedia

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

Articles Figures Tables About

Diazo 1,3-dienes

The diazo-diene (80) was obtained on acetylation (Ac20-py) of D-mannose phenylhydrazone and underwent [4+2]cycloadditions with diethyl azodicarboxylate to give (81) or hydroquinone to give (82) as epimeric mixtures. ... [Pg.130]

A large number of pyridazines are synthetically available from [44-2] cycloaddition reactions. In one general method, azo or diazo compounds are used as dienophiles, and a second approach is based on the reaction between 1,2,4,5-tetrazines and various unsaturated compounds. The most useful azo dienophile is a dialkyl azodicarboxylate which reacts with appropriate dienes to give reduced pyridazines and cinnolines (Scheme 89). With highly substituted dienes the normal cycloaddition reaction is prevented, and, if the ethylenic group in styrenes is substituted with aryl groups, indoles are formed preferentially. The cycloadduct with 2,3-pentadienal acetal is a tetrahydropyridazine derivative which has been used for the preparation of 2,5-diamino-2,5-dideoxyribose (80LA1307). [Pg.48]

Danishefsky s diene 154 DBFOX 232 dendrimers 229 DPT calculations 308 diacetone glucose derived-titanium(IV) 178 diastereoselectivity 216 diazo compounds 242 diazoalkane cycloadditions 278 diazoalkanes 213, 231 (R,R)-4,6-dibenzofurandiyl-2,2 -bis(4-phenylox-azoline) 250... [Pg.330]

In contrast, the structurally similar and equally powerful diene, 3,5-diphenyl-4//-pyrazol-4-one (24), generated in situ by the thermolysis of l,3-bis(diazo)-l,3-diphenylacetone, affords only a modest yield of the [4 + 2] e ifo,ant/-cycloadduct 25.262... [Pg.191]

Cyclizations of doubly unsaturated diazo compounds containing a thiophene ring within rather than at the end of the diene system to yield thicnodiazepines have also been reported. Thus, thermolysis of the sodium salt 7 gives the l//-thieno[3,2-r/]-2,3-diazepine 9. The intermediate 8 rearranges to the more stable product 9 by a symmetry allowed [1,5] shift of hydrogen.14,1... [Pg.363]

Conditions 22 °C molar ratio 800 (diene)/200 (diazo ester)/1 (catalyst)... [Pg.97]

Ishikawa and coworkers reported a synthesis of ( )-0-methylkinamycin C (54) [32, 33]. Their retrosynthetic analysis is shown in Scheme 3.9. It was envisioned that 54 could be derived from the dihydroindanone 55 by D-ring oxygenation, installation of the diazo substituent, and oxidation of the protected hydroquinone function. The dihydroindanone 55 was envisioned to arise from the enol ether 56, itself formed from an endo Diels-Alder reaction between the indenone 59 and the diene 58. [Pg.51]

Coupling of 5-aminobenzotriazole 297 with a diazonium salt derived from 4-methoxyaniline generates diazo derivative 298. Conversion of the amino group into maleinimide produces dye 299 (Scheme 45). Diels-Alder cycloadditions of dye 299 to diene tagged nucleotides allows for their efficient labeling <2002CC2100>. [Pg.40]

Based on his previous work on the catalytic double addition of diazo compounds to alkynes173 using Cp RuCl(COD),174 Dixneuf has developed an efficient one-step synthesis of alkenyl bicyclo[3.1.0]-hexane derivatives of type 163 from enyne precursors 162 (Scheme 43). The catalytic cycle starts with the formation of an Ru=CHR species. It then adds to an alkyne to form ruthenacyclobutene 166, which evolves into vinylcarbene 167. [2 + 2]-Cycloaddition of 167 gives ruthenacyclobutane 168. The novelty in this transformation is the subsequent reductive elimination to give 170 without leading to the formation of diene 169. This can be attributed to the steric hindrance of the CsMes-Ru group. [Pg.321]

C6 and C9 are at opposite ends of a four-carbon unit, but since one of these atoms (C7) is saturated and quaternary, a Diels-Alder reaction is unlikely (can t make diene). The combination of a diazo compound with Rh(II) generates a carbenoid at C9. The nucleophile 06 can add to the empty orbital at C9, generating the 06-C9 bond and a carbonyl ylide at C6-06-C9. Carbonyl ylides are 1,3-dipoles (negative charge on C9, formal positive charge on 06, electron deficiency at C6), so a 1,3-dipolar cycloaddition can now occur to join C2 to C6 and Cl to C9, giving the product. Note how a relatively simple tricyclic starting material is transformed into a complex hexacyclic product in just one step ... [Pg.116]

The (ri" -diene tricarbonyliron)-substituted diazocarbonyl compounds 25 have been found to undergo 1,3-dipolar cycloaddition with methyl acrylate in high yield, but with little or no diastereoselectivity (56). Nevertheless, the facile chromatographic separation of the diastereomeric products 26a,b and 27a,b (Scheme 8.8), permits the synthesis of pure enantiomers when optically active diazo compounds (25) [enantiomeric excess (ee) >96%] are employed. When the reaction of 25 (R = C02Et) with methyl acrylate was carried out at 70 °C, cyclopropanes instead of A -pyrazolines were formed. The enantiomerically pure... [Pg.547]

Various ot,p y,5-unsaturated 1,3-dipoles are known to undergo 1,7-cyclization by a 871-electrocyclization process (329,330), and the corresponding diazo compounds behave similarly. 5-Diazopenta-l,3-diene derivatives such as 285 (Scheme 8.70), generated in situ by thermolysis of the corresponding tosylhydrazone sodium salts, cyclize to form 1,2-diazepines (286) (331). Sharp and co-workers studied the mechanism, scope, and limitations of this transformation. It was found that cis-substitution about the y,8-double bond prevents the 1,7-cyclization and directs the system toward 1,5-cyclization (332,333) (i.e., formation of a 3//-pyrazole), and that the ot,(3-double bond can be part of a phenyl ring (334). In special cases, the y,8-double bond can be incorporated as part of an aromatic [287 288 (335)] or 2- or 3-thienyl ring as well (336). [Pg.600]

Weiss and co-workersprepared a series of oxazohnylidene steroids 343 as luminescence dyes for application as potential intracellular diagnostic agents (Scheme 6.72). The key intermediate 2-aryl-5,5-dimethyl-4(57/)-thiooxazolones 341 were readily available from the corresponding 4(57/)-oxazolones 339. Reaction of 341 with 342, generated in situ from the hydrazone 340, gave 343 as expected. It was not possible to prepare 343 from 3-thio-androsta-l,4-dien-17-one since the requisite corresponding heterocyclic diazo compounds could not be prepared. [Pg.120]

A small amount of anisomeric material is also obtained. The result of this reaction is comparable to the photochemical behaviour of l-diazo-2,3,4,5-tetraphenylcyclopenta-2,4-diene. In contrast, the adduct 8 generates, if pyrolysed in the presence of an excess of triphenyl- or tributyl-phosphine or phosphorus trisdimethylamide, hydrocarbon 10 as the major product this is not observed in the photochemical reaction33. The adducts of diazo compounds and phosphines are normally known as stable ylides34. [Pg.329]

The effect of a chiral substituent at the alkene terminus on the course of the 1,7-electrocyclization of diene-conjugated diazo compounds has also been examined [88TL6361 94JCS(P1)3149]. Cyclization of diazo com-... [Pg.112]

Conjugated dienes, styrenes and electron-rich alkenes are cyclopropanated with ethyl diazoacetate using a triarylamminium salt of appropriate oxidation potential as a cata-lyst/initiator (equation 96)185. These reactions are initiated by electron transfer from the unsaturated substrate to the amminium ion and the double additions of the diazo esters to the conjugated dienes are effectively suppressed. Cyclopropanes geminally bearing two... [Pg.290]


See other pages where Diazo 1,3-dienes is mentioned: [Pg.341]    [Pg.265]    [Pg.127]    [Pg.91]    [Pg.344]    [Pg.390]    [Pg.121]    [Pg.91]    [Pg.116]    [Pg.152]    [Pg.88]    [Pg.60]    [Pg.218]    [Pg.115]    [Pg.127]    [Pg.68]    [Pg.45]    [Pg.571]    [Pg.127]    [Pg.664]   
See also in sourсe #XX -- [ Pg.2 , Pg.4 , Pg.5 , Pg.14 , Pg.16 ]




SEARCH



Diazo-diene intermediate

© 2024 chempedia.info