Cross-coupling allylic compounds

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]. 

Palladium And/Or Copper-Mediated Cross-Coupling Reactions Between 1-Alkynes And Vinyl, Aryl, 1-Alkynyl, 1,2-Propadienyl, Propargyl And Allylic Halides Or Related Compounds. A Review, Rossi. R. Carpita, A. Beilina, F. Org. Prep. Proceed. Int., 1995, 27, 129... 

In the Pd-catalyzed cross-coupling reactions of acylzirconocene chlorides with allylic halides and/or acetates (Section 5.4.4.4), the isolation of the expected p,y-unsaturated ketone is hampered by the formation of the a, P-un saturated ketone, which arises from isomerization of the p,y-double bond. This undesirable formation of the unsaturated ketone can be avoided by the use of a Cu(I) catalyst instead of a Pd catalyst [35], Most Cu(I) salts, with the exception of CuBr - SMe2, can be used as efficient catalysts Thus the reactions of acylzirconocene chlorides with allyl compounds (Table 5 8 and Scheme 5 30) or propargyl halides (Table 5.9) in the presence of a catalytic amount (10 mol%) of Cu(I) in DMF or THF are completed within 1 h at 0°C to give ffie acyl--allyl or acyl-allenyl coupled products, respectively, in good yields. ill... 

The transmetalation of dialkenylchloroboranes of type 52 with methylcopper (3 equiv.) provides an alkenylcopper compound 53, which undergoes cross-coupling with allylic halides to produce mixtures of Sn2 and Sn2 products. Interestingly, this method is also useful for the preparation of functionalized alkenylcoppers such as 54 (Scheme 2.14) [31]. 

Scheme 2.52. Cross-coupling of allylic copper compounds.

Other Pd cross-coupling reactions such as Heck [52] and Suzuki [53] reactions have also been used for macrocyclizations. The main drawback for Pd catalyzed macrocylization is the yield, that is often somewhat disappointing if compared with other established methods. Also, the introduction of the required coupling components (e.g., trialkyltin group, vinylic iodide) can be difficult in some compounds. In other cases, Pd-catalyzed side reactions such as double bond migration or allylic activation can occur. 

When the metallic additive to the intermediate 374 was zinc dihalide (or another Lewis acid, such as aluminum trichloride, iron trichloride or boron trifluoride), a conjugate addition to electrophilic olefins affords 381 . In the case of the lithium-zinc transmetallation, a palladium-catalyzed Negishi cross-coupling reaction with aryl bromides or iodides allowed the preparation of arylated componnds 384 ° in 26-77% yield. In addition, a Sn2 allylation of the mentioned zinc intermediates with reagents of type R CH=CHCH(R )X (X = chlorine, bromine) gave the corresponding compounds 385 in 52-68% yield. ... 

Treatment of the (—)-menthone-derived 2/7-1,3-benzoxazin-4(3//)-one 202 with triflic anhydride gave the triflate 203 in quantitative yield. Palladium-catalyzed cross-coupling of 203 with 2-pyridylzinc halide resulted in formation of an approximately 3 1 mixture of the 4-(2-pyridyl)-2//-l,3-benzoxazine 204 and a 4-imino-l,3-benzodioxane derivative 205 (Scheme 36). Compound 205 was formed by the isomerization of 203, which occurred with complete retention of stereochemistry. The 4-(2-pyridyl)-l,3-benzoxazine derivative 204 was applied in enantioselective allylic alkylations of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate as a chiral ligand inducing a 62% ee in the product <2005JOM(690)2027>. 

Bis[(dimethylisopropoxysilyl)methyl]zinc (74) has proven to be a valuable reagent in the nickel-catalysed cross-coupling reactions with alkenylsulfoximines, giving allylic silanes with complete retention of configuration. An X-ray crystal structure determination of 74 showed this compound to exist in the solid state as a coordination polymer (Figure 41). In 74, in addition to the two covalent Zn—C bonds [Zn—C(l) 1.953(7)... 

Allylboron compounds, synthesis, 9, 170-171 5-Allylboron compounds, cross-coupling reactions, 9, 212 Allylboronic esters, synthesis, 9, 194—195 Allyl boryl ethers, isomerization, 10, 88 Allylchlorodimethylsilanes, for carbonyl allylations,... 

Cross-coupling of allylic compounds occurs by transmetallation between 7i-allyl intermediates and organometallic compounds of Mg, Zn, B, Al, Si and Sn, and subsequent reductive elimination. Reaction of the allylic dithioacetal 180 with MeMgBr in the presence of an Ni catalyst affords alkenes 184 bearing a tert-butyl group [90]. In this reaction, generation of the 7i-allylnickel 181 by oxidative addition and subsequent transmetallation with MeMgBr afford 182. Then the methylated product 183 is formed by reductive elimination, and finally the dimethylated product 184 is formed by the sequence of similar reactions. 

For Pd-catalyzed cross-coupling reactions the organopalladium complex is generated from an organic electrophile RX and a Pd(0) complex in the presence of a carbon nucleophile. Not only organic halides but also sulfonium salts [38], iodonium salts [39], diazonium salts [40], or thiol esters (to yield acylpalladium complexes) [41] can be used as electrophiles. With allylic electrophiles (allyl halides, esters, or carbonates, or strained allylic ethers and related compounds) Pd-i73-jt-allyl complexes are formed these react as soft, electrophilic allylating reagents. 

Hydroboration of allenes 65 with pinacolborane in the presence of Pt(DBA)2 and a trialkylphosphine provides either the allyl boronate 66 or the vinyl boronate 67 regioselectively, depending on the stereoelectronic factors of the phosphine employed (Equation 2) <1999CL1069>. Allyl and vinyl boronates are synthetically important because of their ability to undergo nucleophilic addition to carbonyl compounds as well as transition metal-catalyzed cross-coupling. 

---