Coupling of 1-alkenylboranes with

Coupling of 1-alkenylboranes with 1-bromoalkenes or -alkynes.4,s This reaction fails when catalyzed by Pd(0) alone, but proceeds in high yield in the presence of an added sodium alkoxide or sodium hydroxide in refluxing benzene (or THF). This coupling can be used to prepare (E,E)-, (E,Z)-, (Z,E)-, or (Z,Z)-1,3-dienes stereo- and regiospecifically. 

Recently, Rossi et al. have applied the cross-coupling of 1-alkenylboranes with 1-alkynyl halides for the synthesis of natural products. Thus, (7 , 9Z)-7,9-dodecadien-1-yl acetate (32), the sex pheromone of Lobesia botrana, has been synthesized by the following sequence involving ... 

The decisive step in the stereoselective synthesis of ( )-l-bromo-and (Z)-l-iodo-l-alkenes, which were required for the preparation of various pheromones, consists in the hydroboration of different 1-bromo- and 1-iodoacetylenes [107-109] conjugated alkenynes could be readily prepared by metal-catalyzed cross-coupling of 1-alkenylboranes with 1-bromoalkynes [110]. 

The geometry of both reactants is preserved during the palladium-catalysed cross-coupling of 1-alkenylboranes with 1-alkenyl bromides under strongly basic conditions even when each of the substrates has a Z-configuration (Scheme 67). Under more weakly basic conditions, reactions of this type give mainly head-to-tail coupled products (Scheme 68). °... 

Alkenylboron compounds couple with the representative organic halides or triflates (Scheme 28). Hexaalkylbenzene was synthesized by sixfold alkenylation (55) of hexabromobenzene followed by catalytic hydrogenation of the double bonds 11521. The reaction of 1-alkenylborane with 1-bromo-l-alkyne stereose-lectively provided ( )-enyne (56) which was then converted into ( ,Z)-hexa-deca-10,12-dienal, a sex pheromone of the melonworm 11531. Due to the difficulty of purification of a geometrical mixture, the stereoselective synthesis is critical for such dienes or trienes. The PGEi derivatives (57) were synthesized... 

Miyaura, N., Yamada, K., Suzuki, A. A new stereospecific cross-coupling by the palladium-catalyzed reaction of 1-alkenylboranes with 1-alkenyl or 1-alkynyl halides. Tetrahedron Lett. 1979, 3437-3440. 

As described in the previous section, it was discovered that vinylic boron compounds readily react with vinylic halides to give coupling products. Consequently, we next attempted to examine the reaction of 1-alkenylboranes with haloarenes which have also sp hybridized carbon-halogen bonds, and found that the reaction takes place smoothly. Representative results are exhibited in Table 4. 

Miyaura, N. Yamada, K. Suginome, H. Suzuki, A. (1985) Novel and convenient method for the stereo and regiospecific synthesis of conjugated alkadienes and alkenynes via the palladium catalyzed cross-coupling reaction of 1-alkenylboranes with bromoalkenes and bromoalkynes, J. Am. Chem. Soc., 107,972-80. 

Miyaura, N. Suzuki, A. 1981. The palladium-catalyzed head-to-tail cross-coupling reaction of 1-alkenylboranes with phenyl or 1-alkenyl iodides. A novel synthesis of 2-phenyl-1-aUcenes or 2-alkyl-1,3-alkadienes via oiganoboranes. J. Organomet. Chem. 213 C53-C56. 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

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... 

The procedure described here Is an example of a general method for preparing conjugated alkadienes by the palladium-catalyzed reaction of 1-alkenylboranes or boronates with vinylic halides. Hydroboratlon of l-a1kynes with catecholborane Is a standard method for obtaining (E)-l-alkenylboronates (1). Several different types of alkenylboranes and boronates (2-4) are now available as reagents for the cross-coupling reaction with vinyl halides. 

As described in previous sections, the palladium catalyzed cross-coupling reaction of stereodefined 1-alkenylboranes with stereodefined 1-alkenyl halides in the presence of relatively strong bases such as sodium alkoxides and hydroxide ( head-to-head... 

The coupling of alkenylboranes with alkenyl halides is particularly useful in the stereoselective synthesis of 1,3-diene systems of four possible double-bond isomers... 

Potential difference in reactivity between two G-B bonds allowed the transformation of l,2-bis(boryl)-l-alkenes to 1-alkenylboranes via a cross-coupling with the aryl, 1-alkenyl, benzyl, and cinnamyl halides (Equation (23)).211-213 This tandem procedure synthetically equivalent to a yy/z-carboboration of alkynes was used for synthesizing Tamoxifen derivatives via stepwise double coupling with two of the G-B bonds.212,213 Hydrogenation of the resulting bisborylalk-enes with a chiral rhodium catalyst is synthetically equivalent to an asymmetric diboration of alkenes (Equation (24)).214... 

The above methylcopper-induced reaction is also applicable for cross-coupling of alkenylboranes with organic halides. The treatment of dialkenyichloroboranes (36) with 3 equivalents of n thylcopper at —30 to —40 °C followed by addition of allylic halides gives 1,4-dienes (Eq. 80)In the case of simple alkyl halides, the cross-coupling products are obtained with the aid of PhSLi or P(OPh)3 (Eq. 80)... 

Most recently, it has been disclosed that 1-alkenylboranes react with 3,4-epoxy-1-butene in the presence of a pall ium or nickel complex to form the two corresponding coupling products, 2-ethenyl-3-alken-l-ol (52) and 2,5-alkadien-l-ol (ii) (Eq. 115). ... 

Cross-coupling of aryl halides and 1-alkenylboranes. Aryl iodides and bromides couple efficiently with 1-alkenylboranes (prepared from acetylenes and catecholborane, 4, 70) in the presence of this Pd(0) complex and a base (NaOC2Hs) (equation I). The reaction proceeds with retention of configuration with respect to the alkenylborane to form only (E)-alkenes. Yields are typically 81-100%. One example is reported where the alkenylborane was prepared with disiamylborane (yield 41%)."... 

Cross-coupling reactions between 1-alkynyl halides and 1-alkenylboranes, which are readily available via hydroboration of alkynes, can also be catalyzed by Pd-phosphine complexes. Stereoselective synthesis of conjugated ( )-enynes 143 was achieved by the coupling of the alkynyl bromide with an alkenylborane [Eq. (48)] [69]. 

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