Lithium complexes alkenylation

Allylsilanes result from allyl sulphides which have siloxy subsdtuents with regio and stereochemically using allyl-lithium, from alkenyl Fischer carbene complexes with silanes through addition of Si-H to the carbene, and opdcally active y-silylallylamines result frnn a n-allylPd intermediate obtained from the carbonate using amines or azide, while allyldichlorosilane can be prepared by the direct method at 220 - 320 C as the main product. The protodesilyladon of allylsilanes provides a route to vinyl sulphones while silylmethyl allyl sulphones result from silylmethyl cuprates and sulphonylalka-1,2-dienes, and are used in the... 

Table 1. l-(Diisopropylaminocarbonyloxy)-2-alkenyl-lithium-TMEDA Complexes by Deprotonation of Achiral or Racemic 2-Alkenyl Diisopropylcarbamates with Butyllithium (Selected Examples)... 

It appears that neither the lithium carbenoid pathway nor the cyclopropanation of buta-trienes are general routes to [3]radialenes. More successful is the cyclotrimerization of 1,1-dihaloalkenes via copper or nickel carbenoids, provided the substituents at the other end of the C=C double bond are not too small. Thus, tris(fluoren-9-ylidene)cyclopropane 27 was formed besides butatriene 28 from the (l-bromo-l-alkenyl)cuprate 26 generated in situ from (9-dibromomethylene)fluorene (Scheme 3)10. The cuprate complexes formed... 

For application in organic synthesis, the regiochemistry of insertion of carbenoids into un-symmetrical zirconacydes needs to be predictable. In the case of insertion into mono- and bicydic zirconacydopentenes where there is an wide variety of metal carbenoids insert selectively into the zirconium—alkyl bond [48,59,86], For more complex systems, the regiocon-trol has only been studied for the insertion of lithium chloroallylides (as in Section 3.3.2) [60]. Representative examples of regiocontrol relating to the insertion of lithium chloroal-lylide are shown in Fig. 3.2. 

The lithium-(—)-sparteine complexes, derived from primary 2-alkenyl carbamates, are usually configurationally labile even at —78 °C. During the investigation of the (ii)-crotyl carbamate 301, the (—)-sparteine complex (5 )-302 crystallized in a dynamic thermodynamic resolution process (equation 76) and stereospecific substitutions could be performed with the slurry An incorrect assignment of the configuration of the lithium inter-... 

The same type of addition—as shown by X-ray analysis—occurs in the cationic polymerization of alkenyl ethers R—CH=CH—OR and of 8-chlorovinyl ethers (395). However, NMR analysis showed the presence of some configurational disorder (396). The stereochemistry of acrylate polymerization, determined by the use of deuterated monomers, was found to be strongly dependent on the reaction environment and, in particular, on the solvation of the growing-chain-catalyst system at both the a and jS carbon atoms (390, 397-399). Non-solvated contact ion pairs such as those existing in the presence of lithium catalysts in toluene at low temperature, are responsible for the formation of threo isotactic sequences from cis monomers and, therefore, involve a trans addition in contrast, solvent separated ion pairs (fluorenyllithium in THF) give rise to a predominantly syndiotactic polymer. Finally, in mixed ether-hydrocarbon solvents where there are probably peripherally solvated ion pairs, a predominantly isotactic polymer with nonconstant stereochemistry in the jS position is obtained. It seems evident fiom this complexity of situations that the micro-tacticity of anionic poly(methyl methacrylate) cannot be interpreted by a simple Bernoulli distribution, as has already been discussed in Sect. III-A. 

Before preparation of any a-halo boronic ester is undertaken, it should be noted that two sets of model conditions are outlined in what follows. If the group R1 of the boronic ester 1 is a typical alkyl group, then the rearrangement of the derived borate complex 2 requires a number of hours at 20 C, but if R1 is aryl or alkenyl, then shorter times and lower temperatures are required in order to avoid epimerization of the product 3 catalyzed by zinc chloride and lithium... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Fig. 16.16. Stereoselective preparations of cis-alkenyl-boronic acids and the corresponding diisopropyl ester starting with cis-bromoalkenes. The first step involves a Br/Li exchange to form the alkenyl-lithium compound B. This organolithium compound is subsequently transmetalated to give complex C by using B(0/Pr)3.

Alkynyl(methoxy)borates prepared in situ from an alkynyllithium or sodium and 9-methoxy-9-BBN coupled with 1-alkenyl and aryl halides (Equation (210)).899-902 Addition of triisopropylborate to lithium acetylide yielded an air stable and isolable ate complex that couples with aryl and alkenyl halides (Equation (211)).903 904 Air and moisture stable alkynyltrifluoroborates were probably the most convenient reagents that allow handling in air and coupling reactions in basic aqueous media (Equation (212)).46... 

Noyori et al. proposed that the reaction would be initiated by complexation of the Lewis acidic lithium cation to the ketone oxygen atom then hydride transfer occurs from aluminum to the carbonyl carbon by way of a six-membered chairlike transition state3 (Scheme 4.3c). Between the two competing six-membered chairlike transition states A and B, transition state B is disfavored, due to the substantial n/it-type electronic repulsion between the axially oriented binaph-thoxyl oxygen and the unsaturated phenyl or alkenyl moiety. Although there is a 1,3-diaxial steric interaction between the Al-0 and C-R bonds in transition state... 

It was found that the ate -complex formed by treatment of alkenyl-lithium with trialkylaluminum conjugatively transfers the alkenyl ligand to cyclopentenone in relatively good yield. It is noteworthy that the total yield of the expected product depends on the solvents used. The results — obtained in an analogous reaction — indicate that the addition in hydrocarbons gives as by-products more 1,4-reduction product than cyclopentenone polymer. On the other hand the cyclopentenone derived polymer becomes significant in the more basic THF. The michael addition... 

The observation by Fischer et al.18 that the 4,1-addition of dimethylamine to compound la is thermodynamically controlled at 20°C, whereas 2,1-addition/elimination is kinetically controlled at -115°C, turned out to be limited to few cases.20 It has been shown9a 9b 42 112 113 that for most cases, three competing reaction paths must be considered (i) 2,1-addition/elimina-tion with formation of (l-amino)alkynylcarbene complexes (= 2-amino-l-metalla-l-en-3-ynes) 98 (ii) 4,1-addition to give [(2-amino)alkenyl]carbene complexes (= 4-amino-l-metalla-l,3-butadienes) 96 and (iii) 4,1-addition/ elimination to (3-amino)allenylidene complexes (= 4-amino-l-metalla-1,2,3-butatrienes) 99 (Scheme 33, M = Cr, W). The product ratio 96 98 99 depends on the bulk of substituents R and R1, as well as on the reaction conditions. Addition of lithium amides instead of amines leads to predominant formation of allenylidene complexes 99.112 Furthermore, compounds 99 also can be generated by elimination of ethanol from complexes 96 with BF3 or AlEt3114 and A1C13,113 respectively. 

Reduction of TaCfr with Zn in the presence of aUcyne RC=CR and solvents (L) is believed to yield Ta chloro aUcyne complexes, which react with lithium aUcoxides tethered to alkenyl groups to give chemo- and stereoselective addition of terminal alkenyl groups. Alkoxy-directed insertion of C=C bonds into Ta-aUcyne complexes plays a critical role through the following mechanism. 

Oxidative addition of the carbon-halogen bond is a well-documented reaction for Group 10 transition metal complexes, but it is relatively limited for ruthenium. The example given here involves the reversible oxidative addition of allyl halide to RuCp(CO)2X to produce RuCp(p -allyl)X2 [78]. Oxidative addition of allyl halide to a Ru(0) complex Ru(l,5-COD)(l,3,5-COT) is also reported, but the product yield was poor [79]. Nevertheless, a catalytic Heck-type alkenylation of bromostyrene with methyl acrylate by Ru(l,5-COD)(l,3,5-COT) proceeded smoothly [80]. A cross-coupling reaction of alkenyl halide with Grignard reagents or alkyl lithium also pro-... 

The quasi-complex compounds, as well as the complexes discussed above, led us into a domain which was nearly terra incognita at that time, namely, the substituted (j3-chloro, j8-alkyl, )3-keto) vinyl organometallics. Thus, the simplest of metal vinyls became the objective of our work, and the vinyl, isopropenyl, propenyl, and styryl derivatives of elements such as Hg, B, Tl, Ge, Sn, Si, P, As, Sb, and Bi were studied in collaboration with Freidlina and Borisov. Apart from the procedures mentioned in Section V, vinyl-lithium and vinyl Grignard compounds were used for the synthesis. Note that the highest valence alkenyl derivatives of the type RjSb were reported by us (181-205). 

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