Allene derivatives formation

The formation of 2 furane rings was achieved in one transformation by Ma and co-workers. Allenoic acids and allenyl ketons were reacted in the presence of a palladium catalyst to give the unsymmetrical bifuryl product, arising from the cyclization of both allene derivatives mediated by the same palladium centre followed by their coupling (3.73.) 91... 

Scheme5.35. Formation and silylation of an allene-derived dianion [169].

These reactions are considered to involve insertion of the unsaturated compounds to arylpalladium species followed by the formation of palladacycle intermediates. Oxidative addition of another halide molecule to them leads to the products. In the reaction with norbornene [105 -108] and diphenylacety-lene [109],the corresponding 3 1 and4 1 products and 3 1 product,respectively, are also formed under somewhat different conditions. The mechanisms to account for the formation of these unusual products involving multiple C-H cleavage steps have been proposed. It is noted that, in contrast to Eq. (49), treatment of aryl bromides with aliphatic internal alkynes gives allene derivatives (Eq.50) [110]. 

The reaction of tertiary propargyl sulfinate esters with (MeCuBr)MgCl or (MeCuBr)MgCl -LiBr in THF at 20 C gives rise to the formation of the allenic derivatives in 98% yield through a syn-process [81,82, Eq. (82)]. 

Both l-bromo-3-methyl-l,2-butadiene (182) and 3-bromo-3-methyl-l-butyne (183) give in aqueous ethanol the same product mixture, containing mainly propargyl alcohol and ether, but no allenic derivative (Shiner and Humphrey, 1967). In the presence of both PhS and OH ions, an identical product mixture (32% allenic and 52% propargylic thioether) is again formed from both isomers. This and the rate acceleration by base were ascribed to the formation of a common allene-carbene intermediate which was written as (184a 184b) (Scheme 8). Since the... 

The reaction of allenic derivatives, tetraalkyldiphosphine disulfide and camphorsulfonic acid gave E-2-dialkylthiophosphinoyl-2-alkenes in the presence of RhH(PPh3)4. The reaction involved the P-P cleavage and the transfer of the thiophosphinoyl group to the allenic species with the simultaneous formation of thiophosphinic anhydride (Scheme 19). ... 

Alper and Xiao [45] synthesized thiochromanones by palladiumotalyzed carbonylative ring-forming reactions of 2-iodothiophenol derivatives, allenes, and CO. The fhiochroman-4-ones were achieved in good to excellent isolated yields with high regioselectivity, which was probably caused by electronic effects (Scheme 1.24). This catalytic heteroannulation comprises the regioselective addition of the sulfur moiety on the more electrophilic carbon center of the allene, arylpalladium formation, CO insertion, subsequent intramolecular cydization, and, finally, the reductive elimination. 

Spectra of O-methyloximes of methyl 3,6-diketo-5a- and 3,6-diketo-5/3-cholanoates have been reported by Allen et al. (30). The O-methyloximes, prepared as described by Fales and Luukkainen (49), were found to be particularly useful derivatives since the 5a- and 5 -isomers could be separated by gas chromatography, which was not the case with the free ketones. Considerable differences in relative intensities of the peaks were noted between the spectra of the two isomers. The 5y3 compound gave a base peak at mje 138 (probably ring A) whereas the molecular ion was base peak in the spectrum of the 5a-epimer. These results show the value of O-methyloximes in mass spectrometry of ketonic bile acids. It should be recognized that partial derivative formation may occur, and that formation of syn- and o //-isomers may result in a complex mixture of products from a pure compound. 

In 1999, Alper and Xiao developed a novel access to thiochroman-4-one derivatives by palladium-catalyzed carbonylative heteroannulation of o-iodothiophenols with allenes. The reaction afforded the thiochroman-4-ones in good to excellent isolated yields with high regioselectivity (Scheme 3.76). The catalytic heteroannulation may involve regioselective addition of the sulfur moiety of the reactants on the more positive end of the allene, atylpalladium formation, CO insertion, subsequent intramolecular cyclization, and then reductive elimination. 

In 2006, Gagosz reported the gold-mediated stereoselective synthesis of 2,5-dihydrofurans from butynediol monobenzoates at room temperature. The transformation involved two sequential gold-catalysed reactions the formation of an allene derivative followed by a cyclisation. The reaction was... 

The Larock method for annulation between vicinal iodo-arylamines and 1,2-dienes in the preparation of indoles can be adapted for preparation of azaindoles using corresponding azine substrates. Thus, substituted-3 f-pyrrolo[2,3-fc]pyridin-3-ones can be prepared from 2-amino-3-iodopyridine derivatives by a palladium carboannulation process with al-lenic compounds (Scheme 104). The bicyclic products, the methylene derivatives 308, and the alkylidenes 309 can be oxidatively cleaved with ketone formation. The reaction may proceed by formation of a pyridinylpalladium complex followed by the 7r-allyl complexa-tion of allenic derivatives 310. Since the polar substituents on terminal carbons of the rr-allyl system influence the regiochemistry of the reactions, nucleophilic attack of the nitrogen atom on the most electron-deficient carbon atom of the rr-allyl system affords either of the... 

Finally, allene derivatives were also convenient unsaturated substrates allowing carbon-carbon bond formation from benzylic alcohol via hydrogen transfer processes. With these substrates, the best catalytic systems were based on RuHCl (CO)(PPh3)3 in the presence of an equimolar amount of phosphine ligand such as bis(diisopropylphosphino)ferrocene (dippf) [63], bis(dicyclohexyphosphino) ferrocene or PCyPh2 [64], Some examples of selective formation of homoallylic alcohols using this reaction are reported in Scheme 59. 

Jones R, Tredgold R H, Hoorfar A, Allen R A and Hodge P 1985 Crystal-formation and growth in Langmuir-Blodgett multilayers of azobenzene derivatives—optical and structural studies Thin Solid Films 134 57-66... 

The functionalized allene, DIMETHYL 2,3-PENTADIENEDIOATE, the first in the series, is an intriguing substrate for various addition and cycloaddition reactions. Finally, a new reagent, DI-ferf-BUTYL DICARBONATE, for he formation of A-f-BOC derivatives which eliminates the use o the hazardous fert-BUTYL AZIDOFORMATE (WARNING) is intrqduced. 

All the synthetic protocols described above have limitations to some extent and the yields of the products were modest. In some cases the formation of 1,2-alkadi-enephosphonate derivatives is essential for obtaining the final cyclic products. This is the reason why many authors have used the higher reactivity of 1,2-alkadi-enephosphonates, discovered by Mark [42] in 1962 for the preparation of 2,5-dihydro-l,2-oxaphosphole-2-oxide derivatives. Since then, the oxaphospholic cyclization of 1,2-alkadienephosphonate system of double bonds has become the easiest method for the synthesis of these compounds. The special structure of phosphorylated allenes is responsible for their special properties, which has attracted the attention of chemists for a long time [43 16],... 

The insertion of allenes in the Pd-C bond of cyclopalladated 3-arylisoquinoline derivatives 327 afforded compounds 328, derived from the berberinium cation (Scheme 71). This reaction takes place via the formation of an intermediate (r/ -allyOpalladium complex <2003JOM313>. This chemistry has been extended to the preparation of other cationic N-heterocycles, including naphtho[r+/ ]( uinolizinium derivatives <2004EJ01724>. 

We can narrow the difference from 10 kJmol-1 even further once it is remembered that in the comparison of meso-bisallene, 27, and (Z, Z)-diene, 29, there are two extra alkylallene and alkylolefin interactions for which a stabilization of ca 3 kJ mol-1 for the latter was already suggested. Admittedly, comparison with the corresponding 1,5-cyclooctadiyne suggests strain-derived anomalies. From the enthalpy of hydrogenation, and thus derived enthalpy of formation, of this diyne from W. R. Roth, H. Hopf and C. Horn, Chem. Ber., 127, 1781 (1994), we find 1/2S (bis-allene, bis-acetylene) equals ca — 80 kJ mol-1. We deduce that the discrepancy of this last 5 quantity from the others is due to strain in the cyclic diyne. 

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