- Titanium-mediated addition of grignard reagents to acyl cyanohydrins: Aminocyclopropane versus 1,4-diketone formation
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The 1,2-dianion reactivity of the reagent generated from EtMgBr and titanium isopropoxide was illustrated when N-acyl cyanohydrins were used as substrates (>20 examples), giving both aminocyclopropane derivatives and 1,4-dicarbonyl compounds. When the reaction was performed in diethyl ether, 5-hydroxy-1,4-diketones were the main product. Under specific conditions (use of tetrahydrofuran and a bulky carboxylic moiety), the cyclopropane derivatives were obtained in good yields. The observed dichotomy may be explained by a ring-opening of the five-membered titanacycle intermediate followed by a nonselective acyl addition. The 1,2-dianion reactivity of the reagent generated from EtMgBr and Ti(OiPr)4 was illustrated when N-acyl cyanohydrins were used as substrates (>20 examples). When the reaction was performed in diethyl ether, 1,4-diketones were mainly isolated. Under certain conditions, cyclopropane derivatives were also obtained in good yields. A mechanism rationalizing this dichotomy is presented. Copyright
- Setzer, Paul,Forcher, Gwenael,Boeda, Fabien,Pearson-Long, Morwenna S. M.,Bertus, Philippe
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p. 171 - 180
(2014/01/06)
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- A Systematic Study on the Bakers'Yeast Reduction of 2-Oxoalkyl Benzoates and 1-Chloro-2-alkanones
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The bakers' yeast reduction of a series of 2-oxoalkyl arenecarboxylates (1a-f) (R=CH3 to n-C6H13; X=H) and the phenyl-modified derivatives (1g-l) (R=n-C5H11, X=OH, CH3, F, Cl, Br, or I) as well as 1-chloro-2-alkanones R(C=O)CH2Cl (6a-f) (R=CH3 to n-C6H13) were systematically investigated.The substrate specificities, configuration and percentee of the reduction products were found to be highly dependent on the length of the alkyl group (R) and the α substituent.Thus, the benzoates 1a-f gave optically active 2-hydroxyalkyl benzoates (2a-f) (R, configuration, percentee) (a: CH3, S, 99; b: C2H5, S, 98; c: C3H7, S, 26; d: n-C4H9, R, 55; e: n-C5H11, S, 15; f: n-C6H13, S, 63) in 11-91percent yields.Among the modification experiments of the phenyl group, 1g-l, the p-iodo substituent markedly increased the ee from 15 to 71percent, although the yield was rather lowered (22percent yield).The reduction of α-chloro ketones 6a-f also gave optically active 1-chloro-2-alkanols (7a-f) in 16-69percent yields.
- Sakai, Takashi,Wada, Kou,Murakami, Takahiko,Kohra, Kiichiro,Imajo, Norihisa,et al.
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p. 631 - 638
(2007/10/02)
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- O-Acylation of α-Diazo Ketones. A Novel Route to Alkenediazonium and 1,3-Dioxolium Salts
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O-Acylation of α-diazo ketones with benzoyl triflate or diphenylacetyl triflate generates the corresponding β-(acyloxy)alkenediazonium salts 5 and 15.These thermolabile compounds can be trapped with isopropylamine at low temperature to give triazoles 21.Dediazoniation of 5 and 15 leads to 1,3-dioxolium salts 7 and 16 as well as small amounts of vinyl triflates 8 and 17 via intermediary vinyl cations.O-Benzoylation with benzoyl triflate has also been realized for the quinoid α-diazo ketone 9; the resulting diazonium salt 10 gives triazole 13 on treatment with isopropylamine.
- Lorenz, Wolfgang,Maas, Gerhard
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p. 375 - 381
(2007/10/02)
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