Complex allyl-type

All example for the preparation of diastereomerically pure, but racemic, carbonylchloro(cy-clopentadienyl)-t 3-[l-(l-hydroxyalkyl)allyl]nitrosomolybdenum complexes of type 21 (several examples)6 via the -allyllricarbonyltcyclopentadienylimolybdenum complex 19 is given ... 

A series of complexes of type [Ni(T] -allyl)Cl(NHC)] highlight the important influence of the NHC on the reactivity of the resulting complex towards O. It was shown that 0,-activation is disfavoured when the rotation around the Ni-C, bond is restricted. On the other hand, with complexes displaying free rotation around the Ni-Cj, bond, the complexes react cleanly with O. The overall reaction results in the oxidation of the allyl group and the formation of hydroxy-bridged dimers (Schane 10.4) [14,15]. 

Kondo and Watanabe developed allylations of various types of aldehydes and oximes by using nucleophilic (7r-allyl)ruthenium(ll) complexes of type 154 bearing carbon monoxide ligands (Equation (29)).345 These 73-allyl-ruthenium complexes 154 are ambiphilic reagents and the presence of the carbon monoxide ligands proved to be essential to achieve catalytic allylation reactions. Interestingly, these transformations occur with complete regioselectivity only the more substituted allylic terminus adds to the aldehyde. 

The greater lability of complex 146.C (compared to 145.c), as evinced by the much shorter reaction time, is typical of those that bear a carbomethoxy or acetyl substituent at the central carbon of an i73-allylic ligand. The temperature required for complete decarbonylation of complexes of type 146 and 148 increases with the size of the R-substituent, which suggests a mechanism involving hydride transfer.111 This would also explain the observed activating effect of the centrally located carbomethoxy group in 146.C, which would clearly labilize the methyl proton shown explicitly in 146. 

Replacement of an allylic hydroxyl without saturation or a shift of the double bond was achieved by treatment of some allylic-type alcohols with triphenyliodophosphorane (PhjPHI), triphenyldiiodophosphorane (PhsPIj) or their mixture with triphenyl phosphine (yields 24-60%) [612]. Still another way is the treatment of an allylic alcohol with a pyridine-sulfur trioxide complex followed by reduction of the intermediate with lithium aluminum hydride in tetrahydrofuran (yields 6-98%) [67 J]. In this method saturation of the double bond has taken place in some instances [675]. 

We have developed asymmetric syntheses of isocarbacyclin [3] (Scheme 1.3.2) and cicaprost [4] (Scheme 1.3.3) featuring a Cu-mediated allylic alkylation of an allyl sulfoximine [5-7] and a Ni-catalyzed cross-coupling reaction of a vinyl sulf-oximine [8-10], respectively, transformations that were both developed in our laboratories. The facile synthesis of an allyl sulfoximine by the addition-elimination-isomerization route aroused interest in the synthesis of sulfonimidoyl-sub-stituted aiiyititanium complexes of types 1 and 2 (Fig. 1.3.2) and their application as chiral heteroatom-substituted allyl transfer reagents [11]. 

In the absence of triethylaluminum, the reaction leads to the products of a- and y substilution in the ratio 28 72. Unfortunately reaction of these ate complexes with alkyl halides appears to be limited to benzylic and allylic types, but alkylation at the a-position is highly favored. 

An alternate exocyclic allylic complex of type XIV could produce a cyclic keto carboxy acid, 5 (Figure 7). 

The amphiphilicity and in particular the nucleophilic character of carbon atom C6 of the octadienyl chain in the r 3,r 1-bis-allyl complexes of type B was clearly demonstrated by Tsuji and co-workers [56, 57], who showed that reacting benzal-dehyde with 1,3-butadiene in the presence of a Pd catalyst and PPh3 ligand yields... 

Reactions proceeding according to scheme (10) also account for the effect of Lewis acids or other electron acceptors on catalysts of the 7i-allylic type. The formation of ionic or charge transfer complexes favours the coordination of the conjugated diene as an s-cis-tf ligand, and hence the formation of cis-1,4 monomeric units, if an anti form is predominant [7]. The formation of an ionic complex is shown below, as an example, for 7i-allylnickel chloride and aluminium trichloride [194]. 

Other i73-allyl ruthenium complexes of type 44 have been prepared from la with allylmercury chlorides (allyl, methallyl, crotyl, 1-and 2-phenylallyl, and l-acetyl-2-methylallyl) (45). 

Curtis and Eisenstein355 have made a molecular orbital analysis of the regioselectivity of the addition of nucleophiles to 77-allyl complexes and on the conformation of the 773-allyl ligand in [MoX(CO)2L2(773-allyl)] type complexes. A detailed study of the chirality retention in rearrangements of complexes of the type [MX(CO)2(dppe)(rj3-C3H5)] has been made.356 Studies of the photoelectron spectra,357 electrochemical properties,358 infrared spectroelectrochemistry,359 and fast atom bombardment mass spec-... 

The catalytic cycle proposed for the dimerization of butadiene is shown in Fig. 7.8. As shown by 7.24, two molecules of butadiene coordinate to NiL. A formal oxidative addition, as shown by Eq. 7.8, produces two nickel-carbon bonds and the carbon-carbon bond required for ring formation. The structure of 7.25 with two nickel-carbon bonds (see Fig. 7.8), is a hypothetical one that helps us to understand the carbon-carbon bond formation process. The actual catalytic intermediates that have been observed by spectroscopy have an rf-allyl type of bonding. As shown by reaction 7.9, species 7.25 can reductively eliminate 1,5-cyclooctadiene and the zerovalent nickel complex Ni-L. 

The evidence for the proposed mechanism as shown in Fig. 7.8 comes mainly from in situ NMR studies and X-ray structures of isolated model complexes. Rapid equilibrium between species 7.25 to 7.27 involving an 7j3-allyl type of interaction results in a species of the type 7.28. This species has been observed by NMR. Similar model complexes such as 7.29 and 7.30 have been characterized by single crystal X-ray studies. 

Zwitterionic jr-allylPd complexes of type I may be obtained either from acyclic precursors (1)—usually allylic carbonates having a pronucleophile... 

Pauson-Khand cyclization3k 143 of tV-allyl (l-alkynyl)carbene complexes 134 (M = Cr, W R = Ph, Et R1 = H, Me) affords cyclopentenone derivatives 136144 via cobalt complexes 135145 (Scheme 53), as well as chromium complexes.146 Cyclopentenones also have been derived from 7V-diallyl(l-alkynyl)carbene complexes.39 Stable cobalt complexes of type 135 are obtained from O-allyl (l-alkynyl)carbene complexes. Interestingly, the last-named compounds do not form a cyclopentenone on heating instead, they form an enyne by elimination of M(CO)6 in a retro-Fischer reaction. 147... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

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