Cyclooligomerization reactions

Dale and co-workers examined this reaction in considerable detail some years later and utilized a mixture of HF and BFj in dioxane as catalyst. They noted that this catalyst mixture was stable for months at room temperature and did not etch glass. It was useful for initiating the cyclooligomerization reaction which led to a product mixture. The composition of the mixture was apparently independent of the ethylene oxide concentration and the reaction was apparently not kinetically controlled. 

An entirely different approach was taken by Dale and Daasvatn (see also Sect. 1.4), who isolated 18-crown-6 from a cyclooligomerization reaction of ethylene oxide" . 

Surprisingly, the simplest graphdiyne model, PDM 1, had eluded synthesis. Even though substituted derivatives (e. g. 75,85) have been prepared by the standard cyclooligomerization reaction of o-diethynylbenzenes, isolation of the parent molecule failed via this method [8,51]. Utilization of an intramolecular... 

Whereas PDM 1 in theory could be assembled via the cyclooligomerization reaction, larger, more complex graphdiyne substructures like 91-94 could be constructed only via the intramolecular cyclization route. Scheme 22 illustrates the preparation of 91 [63]. From the outset, the need for solubilizing substituents was recognized thus, the required building blocks (95) were readily prepared by standard transformations. Fourfold in situ desilylation/alkynylation gave the... 

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-... 

While no [4]- and [5]radialenes were formed in the decomposition of cuprate 26, the analogous cuprate generated from l,l-dibromo-2,2-diphenylethene led to the corresponding [4]radialene, and [4]- and [5]radialenes were obtained from the cuprate derived from 22 (see Section II.B and n.C). These findings point to a steric influence on these cyclooligomerization reactions, with sterically demanding substituents favoring the formation of [3]radialenes. 

Fig. 2. Partial reaction potential profiles for cyclooligomerization reactions.

Carbodiimides undergo cyclooligomerization reactions. In this regard they are similar to isocyanates, the mono imides of carbon dioxide. For example, aliphatic carbodiimides undergo rapid dimerization catalyzed by tetrafluoroboric acid at room temperature to give salts of the cyclodimers 183. Neutralization with dilute sodium hydroxide, or better filtration through basic AI2O3, afford l,3-dialkyl-2,4-bisalkylimino-l,3-diazetidines 184. ... 

The cyclooligomerization reaction is not confined to BD as the monomer. Activated or monosubstituted 1,3-dienes also react, but reaction rates are usually slow, and selectivity and turnover numbers (TONs) are low. Cyclotrimerization and cyclodimerization of substituted 1,3-dienes - either alone or in admixture with BD - give numerous isomers of substituted CDT, COD, VCH and divinyl-cyclobutane (DVCB). For example, isoprene [34], 1,3-pentadiene [35], 2,3-dimethylbutadiene [36], 1,3-hexadiene [37], and even 1-vinyl-1-cyclopentene [38] do react (eqs. (2)-(6)). 2,4-Hexadiene is inert. 

Cyclocodimerization and cyclooligomerization reactions of cyclopropenes catalyzed by nickel complexes require alkenes with electron-withdrawing substituents as reaction partners. In this respect, these reactions are complementary to the copper-catalyzed additions discussed in the previous section which do not proceed with electron-poor alkenes due to the low nucleophilicity of the copper-carbene complex. 

In spite of their sterically demanding substituents, the phosphaalkynes chibit an enormous potential for cycloaddition reactions. Even though no intermediates can yet be detected in their thermal cyclooligomerization reactions, the obtained product palette allows the assumption of head-to-head and head-to-tail dimerizations, i.e. [2 + 2]-initiating reactions. 

In the above two examples, oxidative coupling of two olefin molecules occurs. It is likely that the catalysis of numerous cyclooligomerization reactions of unsaturated hydrocarbons proceeds in this manner, as shown for the example of butadiene in Equation 2-54. 

Cyclooligomerization reactions of do- and d(,-ED mixtures have been carried out and found to give do, de, d 2, or d s CDTs (49-51) and do, de, and d 2 cyclodimers (52-54) in nearly statistical ratios—the small deviations from statistic being attributable to secondary isotope effects. This work confirms the idea that the mechanism involves C-C-bond formation without breaking or making C-H bonds. 

In a newly developed reaction, 1,1-reductive elimination of the Pt(dppp) corners from bismetallacycle 4.29 was achieved with iodine with simultaneous C-C bond formation and preservation of the cyclic structure in cyclodimeric terthiophenebutadiyne 4.30 (54 % yield). It represented the smallest (26-membered, [32]annulene) macrocycle in the homologous series, which, however, could never be detected in the previous random cyclooligomerization reactions. 

Of major importance was the finding that cobalt catalysis (typically with CpCo(CO)3 as catalyst) permitted the cocyclooligomerization of functionalized alkynes, the catalyst being, moreover, compatible with functionalities such as ketones, ethers, esters. In this context, Vollhardt [3] even reported a straightforward synthesis of a steroid by a cyclooligomerization reaction of acetylenic precursors (eq. 1). 

A considerable number of large size cycloolefins of macrocyclic nature have become accessible by metathesis cyclooligomerization reaction of small and medium size cycloolefins in the presence of common metathesis catalytic systems [2]. Thus, starting from cyclooctene, Wasserman and coworkers [28] manufactured unsatured carbocycles with up to 120 carbon atoms (degree of oligomerization up to 15) [Eq. (12)]. 

---