- Synthesis of allenes via Nickel-catalyzed cross-coupling reaction of propargylic bromides with grignard reagents
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We describe a convenient method for the synthesis of terminal allenes from cross-coupling of propargylic bromide with Grignard reagent. The reaction of propargylic bromide with 1.2 equivalents of Grignard reagent mediated by Ni(acac)2 (2 mol%) and Ph3P (4 mol%) in THF may produce terminal allenes in good yields and high regioselectivities at room temperature. Georg Thieme Verlag Stuttgart · New York.
- Li, Qinghan,Gau, Hanmou
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experimental part
p. 747 - 750
(2012/06/29)
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- The stereochemistry of the vinylogous Peterson elimination
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Base-induced eliminations of the vinylogous β-hydroxysilanes 7, 9, 11 and 12 are stereospecifically syn, giving largely the trans,trans-diene 8 from 7 and 11, the cis,trans-diene 10 from 9, and the trans,cis-diene 13 from 12. When a cis double bond is produced, it is selectively placed adjacent to the carbon atom that originally carried the hydroxy group. E2′ Reactions with silyl as the electrofugal group and acetate as the nucleofugal group, initiated by fluoride ion, are not stereospecific, but can be highly stereoselective in favour of the trans,trans-diene 8 when the carbon substituent at the silicon-bearing end is a cyclohexyl group and the double bond is cis, and in favour of the trans,cis-diene 13 when the carbon substituent at the silicon-bearing end is a methyl group and the double bond is trans. Attempts to use the Peterson reactions to make o-quinodimethanes stereospecifically failed, with no evidence of 1,4-elimination from the alcohols 40 and 41. The corresponding E2′ reaction from the esters using fluoride ion on the acetates or formates 46 and 47 gave stereoselectively the E,E-quinodimethane 48.
- Fleming, Ian,Morgan, Ian T.,Sarkar, Achintya K.
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p. 2749 - 2763
(2007/10/03)
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- Conversion of alkyl- and arylallenes into 1-alkynes through metallated intermediates
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A number of acetylenes RCH2C≡CH have been obtained by metallation of the allenes RCH=C=CH2 or mixtures of acetylenes and allenes with n-BuLi in THF-hexane and hydrolysis after allowing the metallated allenes to rearrange at roam temperature or by heating under reflux.
- Taherirastgar,Brandsma
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p. 4035 - 4040
(2007/10/03)
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