Allenic Hydrocarbons – Preparation and Use in Organic Synthesis

Hopf, Henning

doi:10.1002/9783527619573.ch5

Modern Allene Chemistry 2004

DOI: 10.1002/9783527619573.ch5

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Allenic Hydrocarbons – Preparation and Use in Organic Synthesis

Henning Hopf¹

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2005

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Cited by 7 publications

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“…There were only a couple of Pt- and Pd-catalyzed asymmetric 1,4-hydrosilylations of 1,3-enynes that have been reported. ,, However, these precious-metal-catalyzed reactions suffered from very limited substrate scopes. Because allenes feature unique structures and diverse reactivities and are valuable multifunctional synthons in synthetic and medicinal chemistry, the development of efficient and selective catalysts for 1,4-hydrosilylation of enynes is highly desired.…”

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Rare-Earth-Catalyzed Selective 1,4-Hydrosilylation of Branched 1,3-Enynes Giving Tetrasubstituted Silylallenes

et al. 2021

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Allenes are versatile synthons in organic synthesis and medicinal chemistry because of their diverse reactivities. Catalytic 1,4-hydrosilylation of 1,3-enynes may present the straightforward strategy for synthesis of silylallenes. However, the transition-metal-catalyzed reaction has not been successful due to poor selectivity and very limited substrate scopes. We report here the efficient and selective 1,4-hydrosilylation of branched 1,3-enynes enabled by the ene-diamido rare-earth ate catalysts using both alkyl and aryl hydrosilanes, leading to the exclusive formation of tetrasubstituted silylallenes. Deuteration reaction, kinetic study, and DFT calculations were conducted to investigate the possible mechanism, revealing crucial roles of high Lewis acidity, large ionic radius, and ate structure of the rare-earth catalysts.

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mentioning

confidence: 99%

Rare-Earth-Catalyzed Selective 1,4-Hydrosilylation of Branched 1,3-Enynes Giving Tetrasubstituted Silylallenes

et al. 2021

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Stereoselective Synthesis of Conjugated Bisallenols as Precursors of Novel Bis(2,5‐dihydrofuran) Derivatives

Poonoth

Krause

2009

Adv Synth Catal

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A stereoselective synthesis of conjugated bis(a-hydroxyallenes) by copper-mediated S N 2'-substitution is described. Their silver-or gold-catalyzed cycloisomerization affords highly functionalized 2-allenyl-substituted 2,5-dihydrofurans and bis(2,5-dihydrofurans) under axis-to-center chirality transfer.Keywords: bisallenes; chirality transfer; cycloisomerization; gold catalysis; silver catalysisThe rich and fascinating chemistry of conjugated bisallenes, [1] a species containing one conjugated and two cumulated diene systems, has inspired chemists in the past decades. Ever since the isolation of the parent 1,2,4,5-hexatetraene (bisallenyl) by Hopf, [2] these have been used as 4p components in [4 + 2] cycloaddition reactions furnishing a wide variety of substituted carbo-and heterocyclic products.[3] These reactions turned out to be an attractive method of preparing [2.2]paracyclophanes as well. [4] The first iron(0)-catalyzed [4 + 1] cycloaddition [5] reaction was also reported using conjugated bisallenes and carbon monoxide furnishing cyclopentenones under mild conditions. Although the chemistry of (unfunctionalized) conjugated bisallenes is very rich, there are only few reports on functionalized derivatives, [3f,6] and no systematic study on the synthesis and transformation of functionalized bisallenes has been reported to date. This is quite intriguing since the development of new methods for the synthesis of functionalized conjugated bisallene derivatives can provide precursors for highly complex carbo-and heterocycles, employing efficient and atom-economical routes.Herein, we disclose a novel, convenient and stereoselective approach to conjugated bis(a-hydroxyallenes), as well as their cyclization to bis(2,5-dihydrofuran) derivatives and 2-allenyl-substituted 2,5-dihydrofurans. We take advantage of the cycloisomerization of a-hydroxyallenes [7] to 2,5-dihydrofurans which is known to occur with axis-to-center chirality transfer when catalyzed by (anhydrous) acid, [8] silver, [9] or gold salts [10,11] -the latter method is often superior in terms of efficiency and functional group tolerance (Scheme 1).We started our approach to bis(a-hydroxyallenes) from (E)-3-methylpent-2-en-4-yn-1-ol which was converted into the bisoxiranes 1a-c by protection, Glaser-Hay coupling (CuCl/TMEDA/O 2 ) [12] and epoxidation with mCPBA. Whereas the NMR spectra show a single set of signals, a slight splitting and/or broadening observed in the HPLC seems to indicate that the bisoxiranes 1 were formed as a mixture of the meso-and dl-diastereomers.[13] All attempts to separate these isomers failed, so that the subsequent reactions were carried out with the mixture. For the allene formation by S N 2'-substitution of propargyloxiranes, various transition metals can be used.[7] Whereas the iron-catalyzed reaction of bisoxiranes 1 with Grignard reagents, [14] as well as the rhodium-catalyzed S N 2'-substitution with arylboronic acids [15] did not afford any of the desired bisallene, we were pleased to observe a smooth conversio...

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