3-Butyn-2-one

When 3-butyne-2-one 7 is used as a Michael acceptor component, a 2,5-cyclohexadienone, e.g. 8, is obtained as the annulation product ... 

Double Michael additions of nitro compounds bearing tethered acidic carbons to 3-butyn-2-one under NaH catalysis give nitrocyclohexanes with high stereoselectivity. The products are transformed into traws-fused bicyclic compounds via the Dickmann reaction on treatment with base. (Eq.4.129).176... 

On the other hand, the involvement of vinyl cationic species in the reaction cannot be ruled out in some cases, as shown in Scheme 4. In this context, it was found that the reaction of 3-butyn-2-one with mesitylene can occur without Pd(OAc)2, clearly indicating the involvement of vinyl cations generated from alkynes and H+ in this reaction.47 1 The yield difference in the presence and in the absence of Pd(OAc)2 may be explained by the competition between [Pd(n)02CF3]+ and vinyl cationic species in the electrophilic substitution of aromatic G-H bonds. Recent kinetic isotope experiments suggest a mechanism involving alkyne coordination to Pd(n) followed by electrophilic aromatic substitution.476... 

Ketones containing triple bonds in the a,)3-positions are reduced to the corresponding unsaturated alcohols with sodium cyanoborohydride or tetra-butylammonium cyanoborohydride in 64-89% yields [780]. Thus 4-phenyl-3-butyn-2-one gave 4-phenyl-3-butyn-2-ol [780]. If the same ketone was converted to its p-toluenesulfonylhydrazone and this was reduced with bis benzyloxy)borane, 1-phenyl-1,2-butadiene was obtained in 21% yield [786]. 

Transition metal-catalyzed intermolecular [2 + 2 + 2] cyclotrimerization of alkynes to benzene derivatives has been extensively studied. In this section, the focus is on the cyclo-trimerizations of the substrates bearing three independent unsaturated bond components. The key issue with this type of process usually involves the challenge of controlling regioselectivity [1—1]. However, 1,3,5-trisubstituted benzene 44 can be obtained as the sole product in good yield when 3-butyn-2-one 43 is used as the substrate for the cyclotrimerization catalyzed by Rh2(pfb)4 (pfb=perfluorobutyrate) in the presence of EtsSiH under a CO atmosphere (Eq. 11) [30]. 

The methyl and ethynyl residues of 3-butyn-2-one (23a) show similar steric demands, making it difficult for reducing reagents to distinguish between the two enantiofacial sides of the substrate. Thus, all methods for reducing 23a fail to afford the enantiopure alcohol 24 [42]. 

Reduction of l-(chloro or bromo) -3-butyn-2-one (27e,f) with recLBADH affords enantiopure R-alcohols 28e,f, resulting in an interesting switch of the enantioselectivity of the enzymatic reduction. As the enantiomers (S) -28e,f can be obtained by recLBADH-catalyzed reduction of 27b-27d and subsequent removal of the si-lyl-protecting group, this enzyme offers unique access to a pair of enantiomers via the same oxidoreductase. Due to the high volatility of the substrates (27e,f) these transformations were only performed on an analytical scale. 

Lewis acids play a dominant role on the chemoselectivity of the cycloaddition of allylsilanes and 3-butyn-2-ones. AICI3 and EtAlCl2 promote [2+2] cycloaddition predominantly, whereas TiCLt-mediated reaction gives significant amount of the [3+2] adduct288,289. The reaction of 2,2-bis(trifluoromethyl)ethylene-l,l-dicarbonitrile with allylsilane without any Lewis acid catalysts yields the cyclobutane derivative via a nonconcerted fashion290. 

The double Michael reaction of 18 was first executed with 4-trimeth-ylsilyl-3-butyn-2-one and catalytic KF 2H2O in EtOH, but side products derived from addition of EtOH to the CN groups of the intermediate 23... 

The enantioselective reduction of 3-butyn-2-one (7) is achieved in 82 % ee by use of the Eapine-Borane 22.9 Application of the commercial available Alpine Borane leads to a lower enantio-selectivity (77 % ee). The mechanism of this reduction is explained in Chapter 13. 

The [2+2] cycloaddition reactions of various 4-dialkylamino-3-butyn-2-ones with substituted phenyl isothiocyanates in refluxing tetrahydrofuran gave access to a series of thietimines 92a-j in poor to satisfactory yields (Table 6) <2001SL361>. As it may be concluded from Table 6, when diethylamine derivatives were replaced by dimethylamine... 

Table 6 [2+2] Cycloadditions of 4-dialkylamino-3-butyn-2-ones with phenyl isothiocyanates...

Aryl isoselenocyanates 4-RC6H4NCSe (R=H, Br, Cl, MeO) (prepared by selenation and dehydration of A-arylformamides) undergo regioselective cycloaddition reactions with 4-diethylamino-3-butyn-2-one in refluxing THF yielding W-arylselenetimines 11 (Scheme 9) <2004H(62)521>. 

The reaction of 2-methyl-3-thioformylindole 173 with 2-aminoethanethiol led to the formation of the 1,3-dithie-tane 176 in 8% yield, and also two Schiff bases 174 and 175 (Equation 28) <1999RJO1507>. The rather exotic reaction of 4-diethylamino-3-butyn-2-one 177 with l-isothiocyanato-4-nitrobenzene 178 has also been reported <2001SL361>. After 4h of heating in THF of the substrates, the substituted thiete 179 and dithietane 180 were isolated in 46% and 35%, respectively (Equation 29) <2001SL361>. 

The hydroarylation of such acetylenic ketones as 3-butyn-2-one 26 poses no problems. In these cases nearly complete E-selectivity was observed, because of isomerization of the kinetically formed Z compounds [2, 4]. Four different electron-rich arenes, ArH, were shown to react smoothly, affording products 27 in yields of 77-96%. 

General Procedure for Hydroarylation of Alkynes 4 and 3-Butyn-2-one 26 by Different Arenes with Ph3PAuCI under Optimized Conditions (Small-scale Experiments)... 

Electrophilic additions with activated alkynes also occur readily with ri2-pyrrole complexes.12bl3b In methanol solution, the pyrrole (20) and 1-methylpyrrole (21) complexes undergo conjugate addition cleanly at C-3 with 3-butyn-2-one to give the p-enone-substituted pyrrole complexes 56 and 58 in high yield (Figure 13). In contrast to what is observed... 

In contrast to MVK or 3-butyn-2-one, the reaction of methyl acrylate with all of the pyrrole complexes studied requires activation of the... 

In the presence of Me2AlCl, isocyclic allylsilane 28 adds to 3-butyn-2-one to afford an ct-enone bearing an allylsilane moiety (Equation (38)).1S1,1Sla In contrast, the ZnI2-promoted ene reaction of an acyclic /3-substituted allylsilane with an a-ynone forms a vinylsilane product exclusively.152... 

The reaction of homochiral allylsilanes with a-enones and a-enals is very valuable for the asymmetric synthesis of multisubstituted cyclopentanes (Equation (40)).161,162 The [3 + 2]-cycloaddition of allylsilanes is applicable to />-quinones163 and />-quinoneimines.164 3-Butyn-2-one undergoes a double cycloaddition with an excess amount of allyltriisopropylsilane to give a bicyclo[3.3.0]octane in good yield (Equation (41)).165... 

The Me2AlCl-promoted reaction of naphthoquinone with 10 at — 78 °C gives [2 + 2]- and [3 + 2]-adducts in 34% and 23% yields, respectively. At 0 °C, a quantitative formation of the latter product is observed.163 When Me AlCl and Znl2 are used as promoters, the reaction of 3-butyn-2-one with certain allylsilanes favors the [2 + 2]-pathway (Equation (47)).151,151a 186 On the other hand, the TiCLj-catalyzed reaction forms [3 + 2]-adducts as shown in Equation (41).165... 

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