Enones reductive coupling with

Preparation of palladium enolates and their reactions (/3-hydride elimination to enones, migratory insertion to C-C multiple bonds, reductive coupling with allyl or aryl groups, etc.) have been reported. However, the nucleophilic addition of palladium enolates to C=0 and C=N bonds has been little investigated.463... 

With an effective strategy for construction of the diazofluorene established, we set out to prepare the coupling partners required for synthesis of (—)-kinamycin F (6). The synthesis of the enone 117 began with meta-cresol (128, Scheme 3.23). Silylation formed the silyl ether 119 in nearly quantitative yield. Birch reduction of the silyl ether 119 formed the cyclohexadiene derivative 129 in excellent yield. Asymmetric dihydroxylation [52] of 129 occurred regioselectively to afford the... 

A total synthesis of functionalized 8,14-seco steroids with five- and six-membered D rings has been developed (467). The synthesis is based on the transformation of (S)-carvone into a steroidal AB ring moiety with a side chain at C(9), which allows the creation of a nitrile oxide at this position. The nitrile oxides are coupled with cyclic enones or enol derivatives of 1,3-diketones, and reductive cleavage of the obtained cycloadducts give the desired products. The formation of a twelve-membered ring compound has been reported in the cycloaddition of one of the nitrile oxides with cyclopentenone and as the result of an intramolecular ene reaction, followed by retro-aldol reaction. 

Though several intermolecular catalytic reductive aldol additions are reported, corresponding reductive cyclizations have received less attention. The first reported reductive aldol cyclization involves use of a (diketonato)cobalt(ll) precatalyst in conjunction with PhSiHj as terminal reductant.48,486 The reductive cyclization is applicable to aromatic and heteroaromatic enone partners to form five- and six-membered rings. As demonstrated by the reductive cyclization of mono-enone mono-aldehyde 65a to afford aldol 65b, exceptionally high levels of ty -diastereoselectivity are observed. Interestingly, exposure of the substrate 65a to low-valent nickel in the presence of excess Et2Zn provides the isomeric homoaldol cyclization product 65c via reductive coupling to the enone /3-position (Scheme 43).47a... 

Polymethylhydrosiloxane (PMHS) has been reported to be a more selective reducing agent when coupled with Pd° catalysts than R3SnH, permitting, for example, the reduction of allylic acetates in the presence of enones and acyl halides (equation 104).300... 

Tertiary amines have also been employed in electron transfer reactions with a variety of different acceptors, including enones, aromatic hydrocarbons, cyanoaro-matics, and stilbene derivatives. These reactions also provide convincing evidence for the intermediacy of aminoalkyl radicals. For example, the photoinduced electron transfer reactions of aromatic hydrocarbons, viz. naphthalene, with tertiary amines result in the reduction of the hydrocarbon as well as reductive coupling [183, 184]. Vinyl-dialkylamines can be envisaged as the complementary dehydrogenation products their formation was confirmed by CIDNP experiments [185]. 

The 1,4-conjugate addition of triorganoindium to enones is promoted by a catalytic amount of Ni(COD)2 (Scheme 8.71) [100], Allylindium reagents can be used in Pd-catalyzed cross-coupling reaction with aryl halides (Scheme 8.72). The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 8.73) [101]. The indium-mediated palladium-catalyzed Ullmann-type reductive coupling of aryl halides proceeds in aqueous media under air (Scheme 8.74) [102]. 

Based on literature precedent, the batch reactor was irradiated for 2 h, affording only 8% of 156 however, on employing a residence time of 2 h within the micro reactor and a flow rate of 8.3 pi min-1, the authors obtained adduct 156 in 88% yield. The enhanced irradiation efficiency obtained within the flow reactor therefore allowed a dramatic increase in reaction yield, coupled with a reduction in the overall reaction time required. With this in mind, the authors investigated the generality of the technique and, as Table 6.15 illustrates, moderate to good yields were obtained for a range of substituted cyclohex-2-enones and vinylic compounds. 

The reaction of /3-stannyl enones with acid chlorides provides 1,4-diketones. This is a reductive coupling. 

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