Mediated coupling conjugated

Scheme 9 Asymmetric hydrogen-mediated coupling of conjugated alkynes to carbonyl compounds and imines...

Stephen L. Buchwald at MIT has reported (Org. Lett. 2004, 6, 4809) a complementary approach. Enantioselective conjugate reduction of the inexpensive 3-methylcyclopentenone 4 led to the silyl enol ether 5, Pd-mediated coupling of which with the aryl halide gave the product 6. 3-Methylcyclohexenone gave the analogous product in 84% . 

Pd-mediated coupling of 50 could, in principle, terminate via p-elimination of either the C8 or C12 hydrogens. However, only the latter was observed. In our case, pentacycle 46 has only the C8 hydrogen available, and the normal course of the Heck reaction would be expected to produce pyridone 58 (Scheme 30). If p-elimination proved slow, an added hydride source might capture the palladium a-complex and provide the desired formal conjugate addition product 51. 

Another interesting tandem Michael initiated sequence was developed in our laboratory by combining the conjugate addition of unsaturated alkoxides to alkylidene malonates with a palladium-mediated coupling reaction with an organic halide. In this cydization reaction, an organopalladium species acts as the electrophilic partner of the cydization. This reaction results in the trans addition of the organopalladium species and of the nucleophile across the unsaturation, and therefore, in overall difunctionalization of the unsaturated substrates [66,67]. 

A range of polycyclic benzo b furans illustrated below was formed by the CuI/TMEDA mediated coupling reaction of conjugated aryl bromide-alkenyl triflates <07TL7578>, and a similar reaction was also found in the synthesis of 5-phenyl morphans <07H(71)881>. 

The nucleoside 3 -triphosphate analogue 117 conjugated to the p-aminophe-nylethylamino linker has been obtained from EDCI-mediated coupling of the... 

One conjugation approach exploited the higher nucleophiUcity of acyl hydra-zides compared to amines during EDC-mediated couplings (39,51,52). This use of difunctional dihydrazides has also been reported to allow facile access to other HA conjugates (Fig. 2). 

Retrosynthetically, a base-catalyzed dimerization of 127 would afford stephacidin B. Avrainvillamide (127) was simplified as vinyl iodide 128 by cleavage of the dihydropyrano [2,3-g]indole-l-oxide moiety and palladium mediated coupling. An aminoacyl radical addition from 129 gave access to 128, while 129 could be derived from cyanide 130 through a hemiaminal formation/dehydration and conjugate addition. Finally, Strecker-like reaction of ketone 131 would fulfill nitrile 130 [55] (Scheme 22). 

A series of soluble polyarylene ethynylene -conjugated poljmiers with M values of 10-15 kDa containing (5,5 -diethynyl-2,2 -bipyridine)Re (COjsCl as part of the polymer backbone have been synthesized by Pd-mediated coupling... 

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