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A regiodivergent silacarboxylation of allenes under a CO2 atmosphere with PhMe2Si-B(pin) as a silicon source in the presence of a copper catalyst at 70 °C has been developed. The regioselectivity of the reaction is successfully rever

The highly selective copper-catalyzed hydroboration of allenes has been developed. Allylboranes and alkenylboranes were selectively prepared by the judicious choice of catalytic species (copper hydride and boryl copper). Furthermore, two types of alkenylboranes could be selectively synthesized by the choice of an appropriate ligand. Mechanistic studies confirmed that the protonation of a (Z)-σ-allyl copper species, which was isolated and structurally characterized by single-crystal X-ray diffraction, was a key step in these reactions. Besides allenes, this method is also applicable to the selective hydroboration of 1,3-diene derivatives to afford allylboranes and homoallylboranes. Copyright

The regioselective radical bromoallylation of allenes proceeded efficiently in the presence of AIBN as a radical initiator to give 2-bromo-substituted 1,5-dienes in excellent yields. The addition of a bromine radical took place regioselectively onto the central carbon of allenes generating a stable allyl radical, which underwent addition/β-fragmentation reactions with allylbromides. The products could be further functionalized by Pd-catalyzed coupling reactions.

A series of benzyl propargyl ethers react with a gold(I) catalyst to furnish variously substituted allenes via a 1,5-hydride shift/fragmentation sequence. This transformation is rapid and practical. It can be performed under very mild conditions (room temperature or 60 °C) using terminal as well as substituted alkyne substrates bearing a primary, secondary, or tertiary benzyl ether group. The allenes thus formed can be reacted in situ with an internal or external nucleophile, corresponding to an overall reductive substitution process, to produce more functionalized compounds.

This paper describes the application of the solution-phase cycloreversion of α-alkylidene-β-lactones as a practical method for the generation of substituted allenes.Upon heating in dimethylformamide solution at 110-125 deg C, these unsaturated β-lac

Selective chemical transformations have been performed on a number of α-methylene β-lactones to illustrate that these highly functionalized heterocycles serve as useful building blocks in organic synthesis.Thus, thermal decarboxylation of these "masked al

β-(Phenylseleno)vinyl sulfones 2 are readily obtained from the free-radical selenosulfonation of acetylenes.Compounds 2 isomerize to allyl sulfones 4 under base-catalyzed conditions in nearly quantitative yield, with high stereoselectivity favoring the Z configuration.Allyl sulfones 4 afford generally high yields of allenic sulfones 1 when subjected to oxidation with m-chloroperbenzoic acid or tert-butyl hydroperoxide, followed by selenoxide syn-elimination.The sulfone-stabilized anion intermediates in the isomerizations of 2 to 4 can be alkylated, deuterated,or silylated in the α-position prior to oxidation, providing allenic sulfones with an additional α-substituent.In some cases, spontaneous elimination of the phenylseleno group occurred, producing the allenic sulfone without the need for an oxidation step.Desulfonylation of allyl sulfones 4f, 4c, and 25 with sodium amalgam afforded vinyl selenides that were converted to allenes in moderate to good yields by oxidation-elimination.The copper catalyzed coupling of allyl sulfones 4 with Grignard reagents comprises an alternative route to vinyl selenide precursors of allenes.These procedures permit the synthesis of various α- and γ-substituted allenic sulfones and allenes from acetylenes.

The boranes I and II, obtained by hydroboration of 1,1-tetra- and 1,1-penta-methyleneallenes with 9-BBN, were used as key reactants in the synthesis of a series of unsaturated gem-substituted carbinols (VIIa-VIIg, Xa-Xc, and XII), as well as 1,1-divinylcy

A useful preparative method for 1,2-dienes from 3-methoxycarbonyloxy-1-alkynes by the palladium-catalyzed hydrogenolysis with ammonium formate is described. 3-Methoxycarbonyloxy-1-alkynes are prepared by the addition of magnesium acetylide to ketones or aldehydes, followed by quenching with methyl chloroformate.

1,2-Dienes were prepared by the selective hydrogenolysis of alk-2-ynyl carbonates with HCO2NH4 catalysed by Pd2(dba)3*CHCl3-P(n-Bu)3 (dba = dibenzylideneacetone).

Benzoic acid and substituted benzoic acids are readily thallated by thallium(III) trifluoroacetate and subsequently reacted with palladium chloride and simple olefins, allylic halides, vinyl halides, or vinyl esters to give isocoumarins.The organic halide reactions are catalytic in palladium. 1,2- and 1,3-dienes also react catalytically to afford 4-alkylidene- and 3-vinyl-3,4-dihydroisocoumarins, respectively.Vinylcyclopropanes also afford 3-vinyl-3,4-dihydroisocoumarins.This highly convenient thallation-olefination approach appears quite general for the synthesis of isocoumarins.

The thermally induced sigmatropic shifts of vinylallenone 7 and vinylallenol 8 were studied.The former (7) rearranges (approximately 100 deg C, 18 h) to previtamin ketone model system 13 in essentially quantitative yield; further thermolysis (approximatel