Insertion involving

For intramolecular N/H insertion involving a (3-lactam, Rh2(OAc)4 was found to be superior to other catalysts and to the photochemical route 300). Therefore, this procedure has been appraised to be the most efficient one for constructing a bicyclic P-lactam and, consequently, has become a standard method for synthesizing... 

Schappacher and Deffieux [15] considered propagation both by an insertion involving a 6-centred transition state [like that favoured by us [2c]] and by an ionic mechanism involving ion-pairs, and considered the latter more likely, thereby ignoring the evidence discussed here. 

The mechanism for 3,1-insertion involves a 2,1-insertion, a (3-hydride elimination at carbon-3, and re-insertion giving a metal-carbon-3 bond. 

Aluminium tri-n-alkyls are dimeric in solution, although - especially for higher alkyls - the fraction of monomer can become significant at higher temperatures [ 19] in the gas phase they are usually monomeric. Kinetic evidence indicates that olefin insertion involves a monomeric aluminium trialkyl this suggests a Cossee-type insertion mechanism. Kinetic data do not indicate the presence of an intermediate olefin 7c-complex [23]. However, if the olefin complexation energy at the 7c-complex stage is low, this would be expected. 

It seems also reasonable to think that substituting TMEDA by PMDT provokes a steric hindrance in the monomer insertion, involving a diminution of reactivity this point is more developed in a coming paper about the polymerization of isoprene with the complexe oligoisoprenyllithium/hexamethyltriethylenetetrami-... 

Insertion involves a transitory a-allyl-bonded chain and -coordinated monomer eventually leading to the re-formation of the rr-allyl chain complex.380-382... 

Intramolecular C—H insertion. The key step in a recent synthesis of pen-talenolactone E methyl ester (3) is the reaction of the a-diazo-p-keto ester (1), prepared in several steps from 4,4-dimethylcyclohexanone, with Rh2(OAc)4. A single product (2) is obtained in high yield even though insertion involves bond formation with a nonfunctionalized carbon atom.4... 

Recently, density functional calculations were performed to determine the nature and stereochemistry of the olefin insertion into the Cu-B bond of (NHC)Cu boryl complexes (NHC = iV-heterocyclic carbene). The theoretical calculations confirm that the mechanism of insertion involves a nucleophilic attack of the boryl ligand on the coordinated olefin. Furthermore, the hyperconjugation of Cu-C (bond angles, which was also experimentally confirmed by the X-ray diffraction studies of these boryl-copper complexes <2007OM2824>. 

Scheme 3. Proposed reaction pathway for the formation of the Wj-jr-allyl,

In the case of the formation of a cycloaliphatic polymer with bicyclic units in the main chain, such as the polymer with poly[methylene-l,3-(2,5-methanocy-clohexane)] structural units obtained in the cyclopolymerisation of 3-vinyl-1,5-hexadiene, the intramolecular insertion, analogous to that presented in scheme (89), is followed by another intramolecular insertion involving a vinyl substituting group ... 

The polymerisation of norbornene occurs in the presence of cationic Pd(II) complexes with weakly nucleophilic ligands via the cis insertion involving predominantly the exo face of the monomer (the diastereotopic endo face of the monomer is much less reactive) [10] ... 

Insertion electrodes — insertion electrodes the electrochemical activity of which relates to insertion processes. Insertion involves two types of materials host materials and guest materials. Host materials provide a framework (lattice) of atoms/molecules, with specific sites such octahedral, tetrahedral, trigonal, or prismatic sites. The guest atoms or ions are inserted electrochemically (by applying an electrical field) and occupy these sites. Insertion can be in most cases reversible, thus leaving most host materials invariant in their physical and chemical properties after an insertion-deinsertion cycle. 

Little work has been reported on insertion of alkynes into Al-H bonds. ( 4119)2 AlH reacts readily with internal alkynes to give uniquely the cis addition product, as expected for a migratory insertion involving concerted addition via a four-center transition state". On the other hand, addition of LiAlH4 to internal alkynes results in trans addition by attack on the triple bond by hydride ion. 

When the initial insertion involves an organotin oxide rather than an alkoxide, the reaction of a second isocyanate molecule induces decarboxylation to give a distannylurea by a process given earlier [reaction (j), 11.5.1], and then a third molecule inserts to give a distannylbiuret ... 

Although there are numerous reactions in which transition metal-silane systems catalytically reduce unsaturated molecules (Section VI.E), the degree to which insertions into M-Si bonds contribute to this reactivity is unclear, since few insertions involving M-Si bonds have been directly observed. This low reactivity toward insertions is consistent with observations that transition metal-silicon bonds are usually shorter than expected, presumably strengthened by rc-bonding between the transition metal and silicon (Section V). Clearly, much work is needed to determine conditions that make insertion reactions favorable. 

Alkyl migrations are not confined to the formation of acyl groups, and, for example, alkene insertion involves the conversion of a coordinated alkene to a cr-bonded alkyl group. Equation 23.37 shows the migration of an H atom related alkyl migrations occur and result in carbon chain growth. 

As with other diazoalkanes, diazomethane reacts with alkenes to form cyclopropane derivatives (sec. 13.9.C.i).272 Reaction with aromatic derivatives leads to ring expansion to cycloheptatriene derivatives.223 Both of these reactions (addition to an alkene or arene insertion) involve generation of an intermediate carbene and addition to a jt bond they will be discussed below. Many of the reactions of diazomethane tend to be ionic in nature and are, therefore, set aside from the other diazoalkane chemistry in this section. One of the commonest uses of diazomethane itself is esterification of small quantities of acids, especially acids that are precious for one reason or another. The reaction is quantitative and gives good yields of a single product, as in Tadano s conversion of 338 to the methyl ester of 339224 in a synthesis of (-)-verrucarol. 

In contrast to the above results, cis addition of nitrogen and metal atoms to alkenes was suggested in Th-catalyzed intramolecular cyclizafion of a,co-aminoalkenes [4b]. Some aminometallation reactions of alkenes or alkynes using aromatic amines also proceeded via cis addition [43,44]. Addition products in Scheme 8.25 and Eq. 8.9 were characterized by X-ray structure determination. The reaction may have proceeded via migratory insertion involving a metal-anilido intermediate, which was an actual starting material in Eq. 8.9. Notice that in this case the alkyne underwent migratory insertion into Pd-N bond, rather than to Pd-C bond. 

A further consideration is that a PUT motion can be accomplished either as an insertion or an alignment. An insertion involves placing one object into another while an alignment involves orienting a part on a surface. Table 9 assists the analyst in better identifying the appropriate case. 

Pyrolysis of [ArC(0)CCo3(CO)9], Ar = aryl, forms [ArCCo3(CO)9], an unusual de-insertion involving a CO ligand and a C—C bond. labeling was... 

---