Intramolecular oligomerization

Olive GH, Olive S, Inter- versus intramolecular oligomerization of nitrile groups in polyacrylonitrile, Polym Bull, 5, 457-461, 1981. 

Ebata, K., Matsuo, T., Inoue, T., et al. (1996) Intramolecular oligomerization of dis-ilalkylenes -Me2Si(CH2)(n)SiMe2- bridged cyclic triacetylenes. Chemistry Letters, 25(12), 1053-1054. 

Another limitation of the traditional Cu-mediated cyclooligomerization reaction is generation of differentially substituted PDMs. In the above case, the substitution pattern in the starting o-diethynylbenzene must be maintained on each and every benzene moiety in the oligomeric mixture of PDMs that is produced. Thus, it is impossible to prepare less symmetric systems like 100 via this route. With the intramolecular synthetic approach, however, it should be possi-... 

Inspired by the well-established nickel-catalyzed co-oligomerization of 1,3-dienes with CO2, which proceeds via bis-TT-allyl intermediate, Mori has developed a powerful intramolecular version of this process (Scheme 103). After insertion of C02 into the bis-vr-allyl complex, a transmetallation with an organozinc reagent takes place to generate the Ni(0) catalyst. Highly functionalized carbo- and heterocyclic compounds with complete stereocontrol can372 be synthesized by this method. 

Side reactions that occur with intramolecular cycloaddition, such as linear oligomerization or dimerization of the nitrile oxide, are not very common when shorter chain lengths n < 1) are used due to the entropically favored intramolecular process. A rather unusual result in this regard involves the formation of a fused cyclooctane instead of the less-strained six-membered ring (also fused) in the cycloaddition of the nitrile oxide derived from p-naphthoquinone (Scheme 6.43). This result is consistent with the effect of electron-withdrawal in the enedione part, leading to increased reactivity (247), and also reflects the known sluggishness of cyclohexenes towards nitrile oxides (cf. Section 6.2.1.2). 

The transformations of o-iodoalkenylbenzenes in the presence of CO and palladium catalysts may involve either carbonylative cylization, or intramolecular Heck reaction, as well as a number of intramolecular pathways leading to oligomeric byproducts. Non-carbonylative pathways can be reasonably suppressed by applying elevated pressures of GO. Under such conditions, the products are formed in good yields, and the predominant termination stage is Pd hydride / -elimination to form exo-cycWc double bond (Equation (27)). 

Based on the formal analogy between the intermolecular hydrovinylation and the intramolecular cycloisomerization process, we have chosen catalysts with proven potential for the first reaction type [48, 51] as the starting point of our study. The results are summarized in Table 2.1.5.7 [64]. Despite its excellent performance in the hydrovinylation of styrene [51], the [ Ni(allyl) Br 2]/(Ra, Sc, Sc)-26/NaBARF system led to disappointingly low conversions and selectivities in the cycloisomerization of 27a (entry 1). Similarly, the [ Ni(allyl)Cl 2]/(Ra,Rc)-4cel/Na-BARF system is not effective for the cycloisomerization of 27a (entry 2) even though it is able to promote the hydrovinylation. The other diastereomer, (R ,Sc)-4cel, however, which forms an active nickel catalyst for styrene oligomerization... 

By its characteristic carbonyl IR absorption band the product of intramolecular termination, i. e. the cyclic B-ketoester was detected by Goode et al. (58), Glusker et al. (59), and Owens et al. (6o) as one of the products of the oligomerization of MMA with phenylmagnesium bromide or fluorenyllithium in toluene. The same compound was found by Lochman et al. (61) when using metalated methylisobutyrate as the initiator in a THF/pentane mixture at high initiator/monomer ratios. 

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