Heck-type olefination

Alkenyliodonium salts can be used as highly reactive substrates for Heck-type olefination and similar palladium-catalyzed cross-coupling reactions [63 -65]. In a recent example, a series of dienes 80 were stereo- and regioselectively prepared by a palladium-catalyzed Heck-type reaction of alkenyliodonium salts 79 with a,/3-unsaturated carbonyl compounds (Scheme 37) [64]. 

Similar to alkenyliodonium salts (see Sect. 6.3), aryliodonium salts are highly reactive substrates in Heck-type olefination and other palladium-catalyzed coupling reactions. Aryliodonium salts can serve as very efficient reagents in the palladium-catalyzed arylations of acrylic acid 101 [75], organotin compounds 102 [76], sodium tetraphenylborate 103 [77], and copper acetylide 104 [78] (Scheme 45). 

Myers AG, Tanaka D, Mannion MR (2002) Development of a decarboxylative palladation reaction and its use in a Heck-type olefination of arene carboxylates. J Am Chem Soc 124 11250-11251... 

Alkenyliodonium salts have been used as highly reactive reagents for Heck-type olefination [39, 971], Sonogashira-type coupling with alkynes [965, 972] and similar other palladium-catalyzed cross-coupling reactions [966, 973, 974]. In a specific example, (Z)-p-fiuoro-a,p-unsaturated esters 721 were stereoselec-tively synthesized from (Z)-2-fluoro-l-alkenyliodonium salts 720 by the Pd-catalyzed methoxycarbonylation reaction (Scheme 3.288) [974]. This reaction proceeds at room temperature and is compatible with various functional groups on the substrate. 

Na, Y, Park, S., Han, S.B. et al. (2004) Ruthenium-catalyzed Heck-type olefination and Suzuki coupling reactions studies on the nature of catalytic species. J. Am. Chem. Soc., 126, 250-8. 

Reactions of aryllead triacetates with olefins (Heck-type reactions) proceed similarly but do not require Cul as co-catalyst. From the numerous reported reactions, that of phenyllead triacetate with 2,3-dihydrofuran is mentioned as a typical example. This affords the C-C coupling product 27 in 68% yield, together with 10% of the homocoupling product (Equation (ll)).47... 

Following our first report on the palladium-catalyzed reaction of vinyl triflates with olefins (Heck-type reaction), oxidative insertion of palladium(O) into the carbon-oxygen bond of easily available vinyl triflates ... 

Narasaka has utilized a Heck-type intramolecular aminopalladation of the olefinic moiety of r,5-unsaturated ketone 0-pentafluorobenzoyloximes 9 to afford 2,5-disubstituted pyrroles 10 (R = CH3, C02Et) <99CL45>. The use of the O-pentafluorobenzoyl group was found necessary to preclude competing Beckmann rearrangements. 

Yoshida and co-workers have reported on the use of alkenyldimethyl(2-pyridil)silanes as versatile platforms for olefin synthesis.The combination of Mizoroki-Heck-type coupling and Hiyama cross-coupling provided a diverse range of stereodefmed polysubstituted olefins. 

Glorius, F. Palladium-catalyzed Heck-type reaction of 2-chloro acetamides with olefins. Tetrahedron Lett. 2003, 44, 5751—5754. 

In this manner, a hydroformylation/condensation sequence of 0-vinyl-anilines give indoles directly. The starting o-vinylanilines are obtained by Heck reaction of the corresponding o-haloanilines. Hydroformylation of these styrene-type olefins proceeds preferably at the benzyl carbon. Intramolecular condensation gives pharmacologically interesting tryptophols and tryptamines in mediocre to good yields (Scheme 12, Table 1) [47]. 

The first step in catalytic reactions of the Heck type is the oxidative addition of the organic halide to Pd(0) species to form an intermediate organopalladium halide constituting the Pd(II) species. This is followed by insertion of the olefinic bond and subsequent /khydrogen elimination [scheme (30)]. The catalyst is recycled by the reaction of the Pd(II)-hydride species with a base [scheme (31)]. It is worth noting here that palladium species, L2(X)Pd—ArCH=CH2, do not propagate the chain growth polymerisation of the CH2=CHArX monomer via its olefinic bond in the discussed process. 

The general catalytic cycle in Heck-type polycondensation consisting of the oxidative addition of aryl halide, olefin insertion and reductive elimination is shown in Figure 8.2 [100-104]. 

The palladium-catalyzed arylation and alkenylation of olefins, which were first discovered in the 1970 s by Heck (7,2) and Mizoroki (3) and have been often called the "Heck reaction", are versatile synthetic means for making a carbon-carbon bond. These reactions have been extensively used for organic synthesis during the past two decades (4-7). However, no reports on the "asymmetric Heck reaction" have been appeared until very recently. Shibasaki reported an asymmetric intramolecular cyclization of alkenyl iodides to give c/j-decalin derivatives of 80-91% ee (8-10). Overman reported an intramolecular cyclization of alkenyl triflate, giving a chiral quaternary carbon center of 45% ee (77). We report herein the first example of intermolecular asymmetric Heck-type arylation of cyclic olefins catalyzed by (7 )-BINAP-coordinated palladium complexes (Scheme 1) (12,13). 

Ruthenium(O) complexes such as Ru(COD)(COT) catalyze the dehydrohalo-genative coupling of vinyl halides with olefins to give substituted conjugated dienes in a Heck-type reaction [11]. Thus, alkenyl halides readily react with activated olefins to produce dienes 16 (Eq. 7). Oxidative addition of vinyl halide, followed by regioselective insertion of an electron-deficient olefin and by -hydrogen elimination leads to the diene. 

A standard Heck reaction, as shown in the example below, involves the palladium-catalysed reaction of a halide with an alkene, most commonly an electron-deficient aUcene such as an acrylate, but other types can also be used. Heck-type cyclisation onto olefins is a useful reaction for ring synthesis. 

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