Organozinc chlorides

Trisubstituted alkenes. The (Z)-2-bromo-l-alkenylboranes (1), obtained by bromoboration of 1-alkynes with BBr, (13, 43), undergo coupling with organozinc chlorides in the presence of Cl2Pd[P(C6H5)3]2 to provide, after protonolysis, disub-stituted alkenes (3). However, the intermediate alkenylborane (2) can undergo a... 

Coupling of vinyl dichlorides.1 This catalyst effects selective coupling of Grig-nard reagents or organozinc chlorides with only one of the chlorine atoms of 1,1-dichloro-l-alkenes (2) to give (Z)-vinyl chlorides (3). The selective coupling involves the chlorine that is trans to the R substituent, probably because of a steric... 

Some synthetically important allenylmetallics, such as allenylzinc and allenylin-dium reagents, are prepared from allenylpalladium intermediates. These reactions are discussed in appropriate sections of this chapter. This section covers the reactions of allenylpalladium compounds without further transmetallation. Allenylpalladium complexes can be prepared from propargylic halides, acetates, carbonates, mesylates, alcohols and certain alkynes [83-87], The allenylpalladium compound prepared from 3-chloro-3-methyl-l-butyne has been isolated and characterized spectroscopically (Eq. 9.106) [83], It was found to couple with organozinc chlorides to produce homologated allenes quantitatively (Eq. 9.107). 

Gore and co-workers developed a convenient experimental procedure for the conversion of a-phosphate-substituted allene 103 to the preferentially formed E-config-ured 1,3-pentadiene 105 (Eq. 14.13) [46, 47, 51]. In a similar manner, Vermeer and co-workers converted a-acetate-substituted allenes 106 into the corresponding 1,3-dienes 107 in moderate to good yields by simple treatment with organozinc chlorides in the presence of Pd(0) catalyst (Eq. 14.14) [52]. 

Fig. 16.26. Pd(0)-catalyzed atkenylations of the organozinc bromides A and B and the organozinc chloride G with the iodoalkene C and the bro-moalkenes D and E, respectively, as an efficient method for the preparation of trans-configured C=C double bonds.

Organozinc chlorides. To avoid generation of dibenzyls during preparation of benzylic zinc reagents from ArCH2Cl in THF, a protocol exploits the beneficial effect of LiCl. Allylzinc chlorides are similarly available, and they add to carbonyl compounds with excellent diastereoselectivity. ... 

The resulting organozinc chloride is then treated with the acid chloride, giving up to 93% yields of ketone.357 For ketone syntheses by means of ethylzinc iodide see Morton, Davidson, and Newey.311... 

Cross-couplings. The coupling bet organozinc chlorides can be promoted b> Pd... 

The Blaise ketone synthesis has been extended to the synthesis of Qf,)0-unsaturated ketones, known as the Blaise-Maire reaction. In addition, the organozinc chloride has been replaced by an organocadmium reagent for a better yield. ... 

Luo and Wang [65] showed that the intermediate palladium(II) species can be trapped by a variety of organozinc chlorides to give exclusively the corresponding (Z)-3-methylene-2,3-dihydroindole derivatives 62-69 in fair to good yields (Scheme 6.18). 

---