- Nickel catalysed coupling of allylamines and boronic acid
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Allylamines function as substrates for cross-coupling with boronic acids in the presence of nickel(0) catalysts rather than palladium(0) catalysts.Aryl-, vinyl- and methyl-boronic acids function well.With vinyl derivatives, E-isomers couple more efficiently than Z-isomer and both fully retain the geometrical integrity.Methylations preferably employ the boronic esters like 2-methyl-1,3,2-benzodioxaborole or 2-methyl-1,3,2-dioxaborolane rather than methylboronic acid.The stereochemistry of the reaction involves a net inversion with respect to the allylamine.The regioselectivity is a function of ligand.Generally, sterically bulky donor phosphines promote new C-C bond formation at the less substituted position.Bidentate ligands, notably 1,1'-binaphthyl-2,2'-ylbis(diphenylphosphinite) (BINAPO), promote new C-C bond formation at the more substituted allyl terminus.The amines appear to be the preferred partner compared to allyl alcohols and esters with the boronic acids and give higher stereospecificity.
- Trost, Barry M.,Spagnol, Michel D.
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p. 2083 - 2096
(2007/10/02)
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- The regiochemistry of the protodesilylation of some cyclopropylmethylsilanes derived from allylsilanes
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Simmons-Smith type methylenation of allylsilanes, followed by protodesilylation, can be used to achieve overall the S(E)2' replacement of the silyl group by a methyl group. The regioselectivity is good for protonation on the methylene carbon of the cyclopropylmethylsilanes 11, 17, 20 and 23, but the low stereoselectivity in the formation of the cyclopropylmethylsilane 26 and its failure to undergo clean protodesilylation make the method of limited use.
- Fleming,Sanderson,Terrett
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- Ring-opening of Some Radicals containing the Cyclopropylmethyl System
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Mono- and bi-cyclic radicals containing the cyclopropylmethyl system are readily generated by interaction of the appropriate halides with triphenyl- or tributyl-stannane.Each radical studied underwent ring-opening by fission of the more substituted βγ-bond.In the case of the secondary radical (12b) the new double bond was formed preferentially in the trans-configuration.Rate constants, which cannot be determined with high accuracy by this method, lie in the range 1E7-3E8 s-1 at 25 deg C.When generated by the flow method in the e.s.r. cavity α-hydroxycyclopropylmethyl radicals undergo β-fission followed by 1,5-hydrogen atom t ransfer to afford enoxyl radicals.The latter reaction occurs more slowly in water than in non-polar solvents.The rigid hydroxynortricyclyl (43) undergoes preferential fission of the less substituted βγ-bond, possibly because of the dipolar nature of the transition state.
- Beckwith, Athelstan L. J.,Moad, Graeme
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p. 1473 - 1482
(2007/10/02)
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