Silyl acetophenone

More recently, further developments have shown that the reaction outlined in Scheme 4.33 can also proceed for other alkenes, such as silyl-enol ethers of acetophenone [48 b], which gives the endo diastereomer in up to 99% ee. It was also shown that / -ethyl-/ -methyl-substituted acyl phosphonate also can undergo a dia-stereo- and enantioselective cycloaddition reaction with ethyl vinyl ether catalyzed by the chiral Ph-BOX-copper(ll) catalyst. The preparative use of the cycloaddition reaction was demonstrated by performing reactions on the gram scale and showing that no special measures are required for the reaction and that the dihydro-pyrans can be obtained in high yield and with very high diastereo- and enantioselective excess. 

Benzaldehyde can be condensed with the N-silylated urethane 671 and aUyltri-methylsilane 82 in the presence of trityl perchlorate to give, via an intermediate 0,N-acetal, the substituted urethane 672 in high yield [197]. 0,N-Acetals such as 673 condense with the enol silyl ether of acetophenone 653 in the presence of TMSOTf 20 to give the co-hydroxyurethane 674 in 94% yield [198] (Scheme 5.62). 

Sila-Pummerer reaction of the /1-ketosulfoxide 1257 with the enol silyl ether of acetophenone 653 in the presence of BSA 22 a and stannous triflate affords the C-substituted sulfide 1258 in 82% yield and HMDSO 7 [52]. The allylic sulfoxide 1259 reacts with 653 in the presence of TMSOTf 20/DIPEA to give the unsaturated sulfide 1260 in 62% yield or, with the enol silyl ether of cyclohexanone 107a , the unsaturated sulfide 1261 in 63% yield and HMDSO 7 [53] (Scheme 8.21). 

Finally, an alternative in situ preparation of the silyl iodide 1789 from tetramethyl-disiloxane 1788 has been described. The silyl iodide 1789 reduces aromatic aldehydes, such as benzaldehyde 1790 a, or ketones such as acetophenone, 1790b, into the iodides 1791 a,b, andquinones 1792 into the hydroquinones 1793 [33] (Scheme 12.11). 

The iodosobenzene HBF4 complex 2022 adds to the enol silyl ether 653 of acetophenone to give the labile iodonium salt 2023, which reacts with cyclohexene or tetramethylethylene to give the adducts 2024 and 2025 [188] (Scheme 12.55). 

OS 75] ]R 4b] ]P 55] For the reaction of 4-bromobenzaldehyde with the silyl enol ether of acetophenone, 100% conversion with respect to the silyl enol ether was achieved in 20 min for a given set of electrical fields (375, 409, 381 and 0 V cm ) [15]. The corresponding batch synthesis time was about 1 day. 

The reduction of ketones or aldehydes with Pl SiFE/KF produces either the mono- or dialkoxydiphenylsilane depending on the stoichiometry of the reaction.75,319 The dendrimeric catalysts 70, 71, or 72 work with I t3Si H to give the silyl ether of acetophenone in excellent yield (Eq. 239).117... 

The reactions of complex 2a with ketones and aldehydes show a strong dependence on the substituents. With benzophenone, substitution of the silyl-substituted acetylene leads to the r]2-complex 58, which is additionally stabilized by a THF ligand. This complex can serve as an interesting starting material for other reactions. With benzaldehyde and acetophenone, the typical zirconadihydrofuran 59, akin to 2c, is obtained from a coupling reaction. This complex is unstable in the case of benzaldehyde and dimerizes, after elimination of bis(trimethylsilyl)acetylene, to yield 60. In this respect, it is similar to the above discussed complex 2c, since both of them show a tendency to eliminate the bis(trimethyl-silyl)acetylene. The reaction of methacrolein with complex 2a depends strongly on the solvent used [40]. 

With the use of NMR spectroscopy Giering and coworkers studied the reaction of acetophenone and HSiBu3 in more detail. The catalyst was [(1,5-cod)RhCl]2 and R-BINAP [36], They noted that the silyl enol ether by-product was formed mainly at the beginning of the reaction and thus this must form via an independent pathway. The common intermediate for silyl ether product and... 

Catalyhc systems based on the commonly used iridium precursor [ Ir(g-Cl)(cod) 2] and diferrocenyl dihalcogenides of L4 and L5 type were also studied in the asymmetric hydrosilylahon of acetophenone, giving a relahvely high yield of sec-phenetyl alcohol silyl ether (I) and a moderate ee of one stereoisomer [49]. 

The cationic complex [Ir(CO)(ic -N,N,N-(S,S)- Pr-pybox)][PF,5] [50] was also found to be catalytically active in the addition of Ph2SiPt2 to acetophenone, with complete conversion of the ketone into the corresponding silyl ether (I) at room temperature after 72 h of reaction. However, desilylation of the product (I) led to racemic 1-phenylethanol, which means that the reduction took place without asymmetric induction. 

Another important variant of the preceding approach is the cycloaddition reaction between monocarbonyl iodonium salt 47 and an alkene to give dihydrofuran 48 (88TL3703 89JOC2605). The iodonium salt 47 is generated by the oxidation of acetophenone silyl enol ether (46) with iodosobenzene in the presence of fluoboric acid. 

In order to obtain further insight into the mechanism of the Mannich-type reaction, sulfone IP and silyl enol ether derived from acetophenone were reacted in the presence HOTf or TMSOTf, which could be produced in the reaction medium when using Bi(0Tf)3-4H20 as catalyst. It appeared that these two compounds efficiently catalyze the Mannich-type reaction (Table 7, entries 2 and 3). The reaction does not occur in the presence of 2,6-di-/<7V-buty I-4-methyl-pyridine [DTBMP] (1.0 equiv. of lp, 1.3 equiv. of silyl enol ether, 0.5 mol% of Bi(0Tf)34H20, 1.5 mol% of 2,6-di-/c/V-buty l-4-methy I-pyridine, 22 °C, 20 h, 99% recovery of lp), which indicates that triflic acid is involved in the mechanism (Table 7, entry 4). 

Je nach Struktur des Substrates kann bei diesem Verfahren auch zweifache Aminome-thylierung (bzw. auch deren Folgereaktionen) eintreten, wie die Bildung von 2-Benzoyl-1,3-bis-[dimethylamino -propan als Hauptprodukt bei der Umsetzung des O-Silyl-enols von Acetophenon unter den gleichen Bcdingungen zeigt. 

ACETONE TRIMETHYLS ILVL ENOL ETHER SILANE, (ISOPROPE NYLOXY )TR IMETHYL SILANE, TRIMETHYL[(1-METHYLETHENYL)0XY]- (1833-53-0), 65, 1 Acetonitrile, purification, 66, 101 Acetophenone Ethanone, 1-phenyl- (98-86-2), 65, 6, 119 Acetophenone silyl enol ether Silane, trimethyl[(1-phenylvinyl)oxy] Silane, tririethyl[(l-phenylethenyl )oxy]- (13735-81-4), 65, 12 4-ACET OXYAZET ID IN-2-ONE 2-AZET IDINONE, 4-HYDROXY-ACETATE (ESTER) 2-AZET ID1N0NE, 4-(ACETYL0XY)- (2 8562 - 53-0), 65, 135 Acetylene Ethyne (74-86-2), 65, 61... 

A photochemical reaction of the silyl enol ether of acetophenone and benzaldehyde provided the 2,3-diphenyl-3-trimethylsilyloxyoxetane (13) with excellent regioselectivity (> 95 5) and diaster-eoselectivity (> 95 5) (91TL7037). In this example, the diastereoselection was explained by anti-approach of the two phenyl groups during the carbon-carbon bond forming step from the diradical intermediate (Scheme 7). 

Initial reports on the use of simple enolates as nucleophiles in TT-allylpalladium chemistry met with only limited success.77 106 The enolate of acetophenone reacted with allyl acetate in the presence of Pd(PPh3)4, but gave predominantly dialkylated product.106 The use of the enol silyl ether of acetophenone gave only monoalkylated product with allyl acetate and Pd° catalysis, but substituted allyl acetates did not function in this reaction.106 Enol stannanes, however, have been found to give monoalkylated products with a wide variety of allyl acetates (equation 19).106 In situ generation of enol stannanes from lithium enolates and trialkylstannyl trifluoroacetates followed by Pd°-catalyzed allylation has been demonstrated.107... 

Acetophenone Ethanone, 1-phenyl- (98-86-2), 65, 6, 119 Acetophenone silyl enol ether Silane, trimethyl[(1-phenylvinyl)oxy]- ... 

Cu(II) and Sn(II) Bisoxazolinc Complexes. Evans has prepared and studied a family of Cu(II) complexes prepared from bisoxazoline ligands [8]. Utilizing these complexes a number of different addition reactions can be successfully conducted on pyruvate, benzyloxyacetalde-hyde, and glyoxylates. Whereas the focus of the work in the context of aldol addition reactions has been on the use of silyl ketene acetals (vide infra), the addition of ketone-derived enoxy silanes 8a-b with methyl pyruvate has been examined (Eq. 8B2.1). The additions of 8a-b proceed in the presence of 10 mol % Cu(II) catalyst at -78°C in CH2Cl2, affording adducts of acetophenone 9a and acetone 9b with 99% and 93% ee, respectively. 

Brunner s group investigated the influence of thermal or photoinduced activation of Fe(Cp) (CO) complexes in the hydrosilylation of acetophenone (4b) with diphenylsilane, forming quantitatively the silylated l-phenylethanol59 (Scheme 4.26) [56,57]. Brunner... 

Since Corey s group first reported 0(9)-allyl-N-(9-anthracenylmethyl) cinchonidi-nium bromide as a new phase-transfer catalyst [13], its application to various asymmetric reactions has been investigated. In particular, this catalyst represents a powerful tool in various conjugated additions using chalcone derivatives (Scheme 3.2). For example, nitromethane [14], acetophenone [15], and silyl eno-lates [16] produce the corresponding adducts in high enantioselectivity. When p-alkyl substrates are used under PTC conditions, asymmetric dimerization triggered by the abstraction of a y-proton proceeds smoothly, with up to 98% ee [17]. 

Further examination of the fluoride ion-catalyzed asymmetric aldol reaction of the enol silyl ethers prepared from acetophenones and pinacolone with benzaldehyde using 4b and its pseudoenantiomer 4c revealed the dependence of the stereochemistry of the reactions on the hydroxymethyl-quinudidine fragment of the catalyst (Table 9.3) [10,15]. 

A similar study on the deprotonation/silylation process of iV-benzyl acetophenone imine led to similar results. Again n-butyllithium was shown to be regioselective. A second deprotonation-trimethylsilylation sequence leads to the expected BSMA derivative.150... 

---