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Bicyclic allenes

Thermolysis of allene 329 with diphenyldiazomethane in benzene afforded 3-benzylthio-l,3,4,4-tetraphenyl-l-butyne 330 and 2,2,3,3-tetraphenylthiirane 331 in 11% and 87% yields, respectively. Thermolysis of bicyclic allene 332 with diphenyldiazomethane under the same conditions as above gave a mixture of thiirane 331, compound 332, 1,3-dithiolane 334, and tricyclic 335 in 12%, 17%, 13%, and 48% yields, respectively (Equations 49 and 50). It was found that heating of a benzene solution of 335 with diphenyldiazomethane gave a mixture of 333 and 334 together with thiirane 331 in 41%, 29%, and 20% yields, respectively <2000JOC1721>. [Pg.369]

The saturated analog, dibromobicyclo[6.1. OJnonane, was not converted to an allene under these conditions, but 10,10-dibromo-cw,cw-tricyclo[7.1.0.0 ]decane (59) did give the analogous, thermolabile, bicyclic allene 60. ... [Pg.2660]

Previous work on intramolecular Sakurai reactions using allylsilanes has now been extended to include propargyl silanes. Using this method a number of bicyclic allene products were prepared in stereoselective fashion (Scheme 49). [Pg.25]

Trapping the bicyclic allene 213 with styrene, 1,1-diphenylethylene, furan and several 1,3-dienes also affords [2+2] cycloadducts, such as 214... [Pg.428]

Allen, J. S. (1981). The Complete Book of Bicycle Commuting. Emtnaus, PA Rodale Press. [Pg.154]

Analogous to the allylsilane cyclizations, alkynylsilanes can also be used to synthesize 1,2-fused bicyclic compounds. The intramolecular addition of 4-[5-(trimethylsilyl)-3-pentynyl]-2-cyclo-hexenone proceeded smoothly in the presence of various Lewis acids, yielding functionalized cw-fused octahydro-5/f-inden-5-ones containing the synthetically useful terminal allene unit45. [Pg.946]

Sulphones (coni.) allenic - see Allenic sulphones allyl - see Allyl sulphones aryl unsaturated alkyl - see Aryl unsaturated alkyl sulphones aryl vinyl - see Aryl vinyl sulphones as radiolytic products 907 bicyclic - see Bicyclic sulphones bis(/ -hydroxyalkyl) - see Bis... [Pg.1206]

A synthetic approach to hyperevolutin A 421, prenylated bicyclo[3.3.1] nonanone derivative, with an acylated phloroglucinol-type fragment, has been described (464). Intramolecular allene-nitrile oxide cycloaddition of 422 has been used to construct the bicyclic framework and the vicinal quaternary centers in cycloadduct 423. [Pg.92]

PtCl2 was shown to catalyze a similar Alder-ene transformation, as in the cycloisomerization of allenyne 117 to triene 118 (Equation (76)).78 In the same study, it was noticed that tetrasubstituted allenes cyclized to bicyclic compounds, such as 120 (Scheme 23), under identical PtCl2 conditions, presumably due to A(1,3) strain in intermediate 119. [Pg.587]

A proposed mechanism of the bis(allene) cyclization involves the formation of the allyl(stannyl)palladium species 6, which undergoes carbocyclization to give vinyl(stannyl)palladium intermediate 7 (Scheme 36). Reductive elimination and cr-bond metathesis may lead to the formation of the m-pentane derivative and the bicyclic product, respectively. The cyclization of allenic aldehydes catalyzed by a palladium complex was also reported.163... [Pg.751]

Addition of Bu3Sn-GeBu3 to bis(allene)s occurs diastereoselectively in the presence of Pd(PPh3)4 to give cis-germastannative cyclization products along with m-fused bicyclic dienes (Equation (128)).297... [Pg.781]

Several routes to the pyrrolo[l,2-f][l,2,3]triazole skeleton have been described. Intramolecular dipolar cycloaddition of azido-alkenes or alkynes seems to be the most convenient process, although the cyclization efficiency seems to be highly substrate dependent (Scheme 16) <2002JA2134, 2003T1477, 2005SL2187, 2005TL8639>. The formation of this bicyclic system by an intramolecular Heck reaction is an attractive alternative. The recent syntheses of sulfamides by intramolecular cyclization of alkenes or allenes offer a complementary route to the classical... [Pg.937]

Although this route to a,cu-diallenes from terminal bisolefmic precursors has often been used in allene hydrocarbon chemistry, the reaction is actually complex and yields product mixtures containing cyclic and bicyclic hydrocarbons when the spacer between the double bond and the allene group is short (between one and three methylene groups), see (a) Th. Miebach, H. Wiister,... [Pg.238]

Cyclic alkynyl carbonates undergo carbonylation in the presence of a palladium catalyst and carbon monoxide (5 MPa) in MeOH to give allenic carboxylates (Eq. 9.118) [92], Bu3P proved superior to Ph3P as the catalyst ligand. An enynyl cyclic carbonate underwent double vicinal carbonylation at 80 °C to produce a five-membered lactone product in 52% yield (Eq. 9.119). When the reaction was performed at 50 °C, the bicyclic enone lactone was produced in 75% yield along with 10% of the y-lactone. [Pg.562]

Dimethyl allene-l,3-dicarboxylate 476 can react with a variety of nucleophiles with an N=C-NH2 substructure to afford monocyclic or bicyclic compounds 501. In this reaction the iminyl nitrogen first attacks the center carbon atom of the allene moiety to afford 3-amino-4-(methoxycarbonyl)-2-butenoate, in which the other nitrogen atom and the conjugated carboxylate undergo an aminolysis reaction to afford the cyclic product [226],... [Pg.672]

The intramolecular dipolar cycloaddition of a nitrone with an unactivated allene was also studied [76], Treatment of 5,6-heptadien-2-one with N-methylhydroxyl-amine in refluxing ethanol yielded allenyl nitrone 78, which cyclized with the terminal allenic C=C bond to give an unsaturated bicyclic isoxazolidine. On the other hand, the site selectivity decreased with an allenic ketone having a trimethylene tether. [Pg.753]

Intramolecular [4 + 2]-cycloaddition reactions of allenic acids and esters proceeded in refluxing toluene to give bicyclic compounds with the exo-isomer predominating (Table 12.9) [120]. When a Lewis acid was used as a promoter, the [4 + 2]-cydoaddi-tion occurred at 0 °C and the endo-isomer was favored. [Pg.773]

About 20 years ago, Bohlmann and co-workers examined South American plants of the widespread Vemonia species and found the first and (until now) only naturally occurring endocydic allenes (Scheme 18.32) [97]. These are the bicyclic sesquiterpene lactones 100-102 bearing a 10-membered ring [98], in which the E-double bond of the larger ring can also be present in its oxidized form (101, 102). As in other cases, these fasdnating natural products have not been synthesized until now. [Pg.1017]

Wender et al. s [5 + 2] metal-catalyzed annulation strategy has also been applied to the total synthesis of (+)-aphanamol I (154) [34]. The scope of this method was expanded by using a tetrasubstituted allene that resulted in the stereoselective formation of an angular methyl group. The reaction of allene 149 with 0.5 mol% of rhodium biscarbonyl choride dimer afforded the fused bicyclic product 152 in 93% yield with complete exo/endo and diastereoselectivity (Scheme 19.28). The stereoselectivity of this process was attributed to a preference for formation of the cis-fused metallo-... [Pg.1061]

Tetramethylene-ethane (TME), or 2,2/-bis-allyl diradical 81, was suggested as an intermediate in the thermal dimerization of allene, as well as in the interconversions of 1,2-dimethylenecyclobutane 82, methylenespiropentane 83, bis-cyclopropylidene 84 and other bicyclic systems (equation 30)45. The isolation of two different isomeric dimethylene cyclobutanes 87 and 88 (in a ca 2 I ratio) after the thermal rearrangement of the deuteriated 1,2-dimethylene cyclobutane 85 suggests that the rearrangement proceeds via a perpendicular tetramethyleneethane diradical (2,2/-bisallyl) 86 (equation 31)45. [Pg.753]

Allenyne represents an interesting substrate for the intramolecular Pauson-Khand(-type) reaction, where an allene moiety acts as an ene component. Here, there are two possible reaction pathways (Scheme 11.21) (i) the reaction of an external tr-bond of allene moiety gives a bicyclic dienone (type A) or (ii) the reaction of an internal 7i-bond gives a bicyclic cyclopentenone with an alkylidene substituent (type B). [Pg.285]

Although all of the reported Rh-catalyzed reactions of allenynes were of type A, an Ir catalyst resulted in a different regioselectivity. That is, when allenynes with two substituents on the allene terminus were used under a low partial pressure of CO, the type B reaction proceeded exclusively such that bicyclic cyclopentenones with an aLkylidene substituent were obtained (Scheme 11.22) [34]. However, when [RhCl(CO)(PPh3)2] was used as a catalyst under the same reaction conditions in place of [IrCl(CO)(PPh3)2], the type A reaction was predominant These results imply that the metal centers of the catalysts control the regioselectivity of two ole-finic moieties of allene to some extent... [Pg.287]

Recent advances in the rhodium-catalyzed [4-1-2] reactions have led to the development of the first highly regioselective intermolecular cyclization, providing access to new classes of carbocycles with both activated and unactivated substrates. The chemo- and stereoselective carbocyclizations of tethered diene-allene derivatives afford new classes of 5,6- and 6,6-bicyclic systems. Additionally, examination of a wide range of factors that influence both diastereo- and enantioselectivity has provided a significant advance in the understanding of catalyst requirements across these systems. [Pg.260]


See other pages where Bicyclic allenes is mentioned: [Pg.797]    [Pg.797]    [Pg.57]    [Pg.797]    [Pg.797]    [Pg.57]    [Pg.337]    [Pg.1036]    [Pg.98]    [Pg.103]    [Pg.211]    [Pg.311]    [Pg.50]    [Pg.935]    [Pg.201]    [Pg.367]    [Pg.715]    [Pg.724]    [Pg.1013]    [Pg.1015]    [Pg.1062]    [Pg.1083]    [Pg.1120]    [Pg.30]    [Pg.741]    [Pg.746]    [Pg.203]    [Pg.106]    [Pg.245]   
See also in sourсe #XX -- [ Pg.428 ]




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