Cross-coupling reactions with alkynyl, alkenyl, and aryl halides

2 Cross-coupling Reactions with Alkynyl, Alkenyl, and Aryl Halides 

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Oxidative addition [1, 38] of 1-alkenyl, 1-alkynyl, allyl, benzyl, and aryl halides to a palladium(O) complex affords a stable trans-o-p al 1 adi u m( 11) complex (11). The reaction proceeds with complete retention of configuration for alkenyl halides and with inversion for allylic and benzylic halides. Alkyl halides having /5-hydrogens are rarely useful because the oxidative addition step is very slow and may compete with /5-hydride elimination from the <7-organopalladium(II) species. However, it has been recendy shown that iodoalkanes undergo the cross-coupling reaction with organoboron compounds (Section 2.4.5). 

The intermediate alkenylzirconium compounds can be used in a cross-coupling reaction with alkenyl, aryl, or alkynyl halides in the presence of Pd or Ni catalysts and ZnCU. ... 

Phenethylzinc(II) bromide (PhCH2CH2ZnBr) is widely used in homobenzyUc couplings with aryl halides and alkenyl halides to generate 1,5-dienes [35c, 219-221]. Homoalkenyl- and homopropargylzinc halides are also reported to react with aryl halides [35c, 222, 223]. Recent examples of Pd-catalyzed cross-coupling reactions with aryl or alkenyl halides are highlighted in Scheme 3.57. However, the use of alkynyl halides in these reactions does not appear to have been reported [18c]. 

The Negishi palladium-catalyzed cross-coupling reaction of alkenyl, aryl, and alkynyl halides with unsaturated organozinc reagents provides a versatile method for preparing stereodefined arylalkenes, arylalkynes, conjugated dienes, and conjugated... 

The palladium-catalyzed reaction of alkenyl-, aryl-, alkynyl- and alkylsiloxanes with aryl, alkyl, and alkenyl halides and triflates in the presence of activators is known as the Hiyama cross-coupling reaction and several reviews have been published. This chapter will present major developments and examples of recent carbon-carbon bond formation methodology and improvements as well as their use in natural products synthesis in the last few years. 

Many reviews have been published in the last few years on the applications of the Hiyama cross-coupling reaction in organic synthesis. In general, preparation of biaryls or heterobiaryls is the most common application of this reaction since new methodology development is based on examples of these. The most prevalent applications of the aryl and heteroaryl halides with organosilane precursors involve reactions such as vinylations, alkenylations, and alkynylations. The reader is encouraged to consult these key reviews. This section will describe some of the more recent applications published in the last few years. 

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