Efficient synthetic method of multisubstituted allenes from the reactions of allylindium reagents with 3 degree-propargyl alcohols

An efficient synthetic method of tri- and tetra-substituted allenes having an allyl and methallyl group was developed by the reactions of allylindium reagents generated in situ from indium and allyl bromides with 3 degree-propargyl alcohols.     

Stereoselective synthesis of allylsilanes from chloromethylsilylalkynes

Regio- and stereoselective hydralumination of 1-chloromethyldimethylsilyl-1-alkyne with DIBAH affords (Z)-1- chloromethyldimethylsilyl-1-diisobutylalumino-1-alkene which gives (E)-1-trimethylsilyl-2-alkene as a sole product by successive treatment with 3 equiv of methyllithium and water. Reaction of the organoaluminium intermediate with trimethyl-aluminium in refluxing heptane produces a mixture of (Z)- and (E)-1-trimethylsilyl-2-alkene.     

Novel rearrangement of chloromethylvinylsilanes into allylsilanes. Stereoselective synthesis of metallated allylsilanes from 1-alkynes

Regio and stereoselective hydralumination of 1-(chloromethyldimethylsilyl)-1-alkyne with diisobutylaluminium hydride (DIBAH) affords (Z)-1-(chloromethyldimethylsilyl)-1-(diisobutylalumino)-1-alkene. Treatment of the aluminium-substituted vinylsilane with 3 equivalents of methyllithium affords (E)-1-(trimethylsilyl)-2-lithio-2-alkene as a sole product. Reaction of aluminium-substituted vinylsilane with trimethylaluminium in refluxing heptane produces a mixture of (E)-1-trimethyl-silyl-2-alumino-2-alkene and 2-trimethylsilyl-1-alkene. Reaction of 1-(chloromethyldimethylsilyl)-1-alkyne with triisobutylaluminium gives 2-(isobutyldimethylsilyl)-1-alkene exclusively. Reactions of the lithiated allylsilane with several electrophiles give the corresponding carbometallated products, allylsilanes bearing alkyl, allyl, vinyl, or alkoxycarbonyl groups. Protodesilylation of 3-(trimethylsilylmethyl)-1,3-decadiene gives 3-methylene-1-decene selectively. Reaction of trialkylaluminium with trimethylsilylethyne gives bistrimethylsilylated diene by successive addition of silylethyne to the aluminium reagent; in contrast, chloromethyldimethylsilylethyne gives the mono-adduct regio and stereoselectively.     

Preparation of carbocycles via base-catalyzed endo-mode cyclization of allenes

A new and reliable procedure for constructing five- to seven-membered carbocycles via an endo-mode ring-closing reaction of 1-phenylsulfonylallenes with a substituent that has a terminal active methine moiety at the C1-position has been developed. Trisubstituted 1-phenylsulfonylallenes underwent a similar endo-mode ring-closing reaction to produce the corresponding five- to seven-membered carbocycles, while the formation of six- and seven-membered carbocycles from the corresponding tetrasubstituted allene was not realized. In addition, the introduction of an aromatic ring to the alkyl side chain of the starting allenes made possible the construction not only of normal-sized carbocycles but also an eight-membered framework.     

Preparation and electrophilic cyclization of multisubstituted dienamides leading to cyclic iminoethers

Stereodefined multisubstituted dienamides could be concisely prepared in high yields by direct addition of 1-lithiobutadiene derivatives to both N-aryl and N-alkyl isocyanates. Electrophilic cyclization of these dienamides was achieved to generate substituted cyclic iminoethers in excellent yields with perfect selectivity. When treated with 12 N aqueous HCl, dienamides underwent efficient and selective electrophilic cyclization to afford cyclic imidate derivatives. When treated with NBS, monobrominated or double-brominated cyclic iminoethers were formed.     

Practical synthesis of allylsilanes from 1-benzenesulfonyl-2-trimethylsilylethane

the methanesulfonates of the adducts of aldehydes and ketones with l-(l-benzene-sulfonyl-2-trimethylsilyl) ethyllithium are converted by sodium-amalgam to allylsilanes     

Titanocene-catalyzed formation of allylsilanes from allyl ethers and chlorosilanes

A new method for silylation of allyl ethers with chlorosilanes has been developed by the use of Cp₂TiCl₂ as a catalyst. This reaction proceeds efficiently at −20 °C in THF using ⁿBuMgCl. A plausible reaction pathway via allyltitanocene intermediate was proposed.     

Phenylselenodesilylation of allylsilanes and regiospecific transformation of allylsilanes to allylic alcohols via allylselenides

Allylsilanes were converted regiospecifically to allylselenides by reaction with phenylselenenyl chloride and subsequent treatment with anhydrous tin(II) chloride or florisil. Oxidative work-up of these allylselenides gave the corresponding allylic alcohols regiospecifically.     

Palladium-catalysed synthesis of allyl acetates from allenes

Allyl acetates were synthesised from allenes utilising methodology based on the general reactivity of π-allyl palladium intermediates which participate efficiently in transformations involving nucleophiles. Reactions of allenes and aryl iodides in the presence of AcONa and Pd(OAc)₂/PPh₃ as the catalytic system afforded allyl acetates in moderate to good yields. Monosubstituted allenes, depending on their structure, produced either a separable mixture of two regioisomeric products or a single regioisomer. As allylic acetates can be easily hydrolysed, the methodology is applicable for the synthesis of allyl alcohols as well.     

Preparation of CF3-containing 1,3-di- and 1,1,3-trisubstituted allenes

Novel synthetic pathway to access trifluoromethylated allenes with 1,3-di- as well as 1,1,3-trisubstitution patterns was developed from a variety of 4,4,4-trifluorobut-2-yn-1-ols which were then transformed into the corresponding vinylic iodides in highly regio- and stereospecific manners, and zinc-mediated beta-elimination after trifluoroacetylation of the hydroxyl group eventually realized the formation of the target molecules in good to excellent overall yields in facile and short steps.     

Preparation of vinyl allenes from 1-lithio-1,3-dienyl phosphine oxides and aldehydes by the Wittig-Horner reaction

[reaction: see text] Vinyl allenes were prepared in high yields by the Wittig-Horner reaction of 1-lithio-1,3-dienyl phosphine oxides with aldehydes. 1-Lithio-1,3-dienyl phosphine oxides were generated in situ from lithiation of 1-iodo-1,3-dienyl phosphine oxides, which were obtained by iodination of alpha-phosphinozirconacyclopentadienes. As a whole, a vinyl allene is synthesized from two different alkynes and one aldehyde.     

Fluorine-containing allenes

Conclusions Tetrakis(trifluoromethyl)allene reacts with DMF at 20° to give hexafluoroisobutenyldimethylamine.See [1] for Communications 5.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1326–1327, June, 1976.     

Synthesis of novel enantiopure fluorinated building blocks from acyclic chiral allylsilanes

[reaction: see text] Homochiral beta-fluorinated gamma,delta-unsaturated carboxylic acids with an allylic fluorinated stereogenic center are available from the corresponding enantiopure allylsilanes. The key step for introduction of the fluorine substituent is an electrophilic fluorodesilylation reaction carried out in the presence of Selectfluor. Reduction of the resulting beta-fluorinated pentenoic acid into the corresponding fluorinated alcohol was also performed leading to the formation of an enantiopure second-generation fluorinated building block.     

Distinguishing carbones from allenes by complexation to AuCl

Quantum chemical calculations have been performed for the dicoordinated carbon compounds C(PPh(3))(2), C(NHC(Me))(2), R(2) C=C=CR(2) (R = H, F, NMe(2)), C(3)O(2), C(CN)(2)(-) and N-methyl-substituted N-heterocyclic carbene (NHC(Me)). The geometries of the complexes in which the dicoordinated carbon molecules bind as ligands to one and two AuCl moieties have been optimized and the strength and nature of the metal-ligand interactions in the mono- and diaurated complexes were investigated by means of energy decomposition analysis. The goal of the study is to elucidate the differences in the chemical behavior between carbones, allenes and carbenes. The results show that carbones bind one and two AuCl species in η(1) fashion, whereas allenes bind them in η(2) fashion. Compounds with latent divalent carbon(0) character can coordinate in more than one way, with the dominant mode indicating the degree of carbone or allene character. The calculated structures of the mono- and diaurated tetraaminoallenes (TAAs) reveal that TAAs exhibit a chameleon-like behavior: The bonding situation in the equilibrium structure is best described as allene [(R(2)N)(2)]C=C=C[(NR(2))(2)] in which the central carbon atom is a tetravalent C(IV) species, but the reactivity suggests that TAAs should be considered as divalent C(0) compounds C{C[(NR(2))(2)]}(2), that is, as "hidden" carbones. Carbon suboxide binds one AuCl preferentially in the η(1) mode, whereas the equilibrium structures of the η(1)- and η(2)-bonded diaurated complex are energetically nearly degenerate. The doubly negatively charged isoelectronic carbone C(CN)(2)(2-) binds one and two AuCl very strongly in characteristic η(1) fashion. The N-heterocyclic carbene complex, [NHC(Me)(AuCl)], possesses a high bond dissociation energy (BDE) for the splitting off of AuCl. The diaurated NHC adduct, [NHC(Me)(AuCl)(2)], has two η(1)-bonded AuCl moieties that exhibit aurophilic attraction, which yield a moderate bond strength that might be large enough for synthesizing the complex. The BDE for the second AuCl in [NHC(Me)(AuCl)(2)] is clearly smaller than the values for the second AuCl in doubly aurated carbone complexes.