Alkenyl chlorides coupling reactions

Some of the notable recent developments in the Pd- or Ni-catalyzed aryl-alkenyl and alkenyl-aryl coupling reactions include the use of aryl and alkenyl chlorides along the lines of earlier discussions. lust a couple of representative examples of the aryl-alkenyl coupling reaction with alkenyl chlorides are shown in Scheme 33. 

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. 

Aryl chlorides can also be used as coupling partners for azabismocine reagents 2. In the coupling reaction with aryl chlorides, Pd(PPh3)4 was not an efficient catalyst, and Pd(OAc)2/l,l,-bis(diphenylphosphino)ferrocene (dppf) combination was found to be effective [54]. Not only the arylation, but also methylation, alkenylation and alkynylation reactions can be accomplished by using the corresponding bismuth compounds (Scheme 35). The addition of CsF improved the product yields. However, electron-rich aryl chlorides were unable to be coupled efficiently under these reaction conditions. 

Organobismuth compound 1" was also used for the cross-coupling reaction with alkenyl triflates. CC Et-substituted cyclopentenyl triflate afforded the coupling product quantitatively, while the sterically hindered triflate gave the product in poor yield (Scheme 39) [44], Azabismocine 2 reacted with activated alkenyl chlorides to give the coupling products in moderate to good yields (Scheme 40) [54],... 

Scheme 40 Cross-coupling reaction of phenylazabismocine with alkenyl chlorides...

When the first electrophile was not a ketone or an aldehyde, as illustrated for the reaction of 276 with crotonyl chloride, the intermediate chelated alkenylmetal 278 could also be subjected to iodinolysis or palladium-catalyzed cross-coupling reactions with aryl and alkenyl iodides in the presence of a stoichiometric amount of CuBr as a promotor as well as a polar cosolvent such as IV, IV-di methyl acetamide (DMA) (equation 131)165 166. 

A variety of fluorinated alkenyl zinc reagents such as CF2=CFZnCl, CF2=CHZnCl, E and Z-RCF = CFZnCl have been prepared by the first method (Scheme 54). In the presence of palladium catalyst, these fluorinated alkenyl zinc reagents undergo cross-coupling reactions with aryl iodides, vinyl iodides, acid chlorides and 1-iodo-l-alkynes to give the corresponding fluorinated alkenyl derivatives [127, 146-153], which have been utilized in the synthesis of fluorinated codlemones [154]. Typical examples are outlined below (Scheme 55). 

The coupling reaction with active halides such as allyl halides or acid chlorides catalyzed by cuprous halides afforded the corresponding alkenylated compounds [131,167,168] (Scheme 57). 

The palladium-catalyzed cyclizative coupling reaction of a-allenols 41 with alkenyl halides was also explored. The transformation of allenols 41 into spirocyclic disubstituted dihydrofuran (3-lactams 43 was readily achieved in high yields, by treatment with allyl bromide or 2,3-dibromopropene in the presence of palladium (II) chloride (5 mol%) (Scheme 14) [60]. 

Alkynylsilanes can be converted into alkynylcoppers by treatment with Cu salts in an aprotic polar solvent such as l,3-dimethyl-2-imidazolidinone (DMI).62 The Cu-promoted coupling reactions via the Si-Cu transmetallation of alkynylsilanes are valuable for the syntheses of alkynyl ketones, 1,3-diynes, 1,3-enynes, and 1-aryl-l-alkynes from acid chlorides,62 alkynyl chlorides,63 alkenyl iodides,64 and aryl iodides,64 respectively (Equation (12)). In addition, symmetric 1,3-diynes can be prepared by the CuCl-mediated homocoupling of alkynylsilanes.65 653... 

---