Macrocyclization, intramolecular

The polymerization of ethyleneimine (16,354—357) is started by a catalyticaHy active reagent (H or a Lewis acid), which converts the ethyleneimine into a highly electrophilic initiator molecule. The initiator then reacts with nitrogen nucleophiles, such as the ethyleneimine monomer and the subsequendy formed oligomers, to produce a branched polymer, which contains primary, secondary, and tertiary nitrogen atoms in random ratios. Termination takes place by intramolecular macrocycle formation. 

Simanek el al. investigated the structure dependence of the kinetics of thiol-disulfide exchange reactions.[44] In general, the rate of exchange decreased as the size of the dendrimers increased. Dendrimers with disulfides attached near the core undergo exchange more slowly than dendrimers with disulfides at the periphery. No evidence was found for intramolecular macrocyclization (cooperative) exchange. 

The copper acetate-mediated inter- and intramolecular O-arylation of phenols with phenylboronic acid was the key step in the preparation of natural or macrocyclic biphenyl ethers. The intramolecular macrocyclization was mild and tolerant of chemical functionality (Equation (238)). The protocol has been used for the synthesis of (—)-teje-... 

Fig. 14 (a,b) Intramolecular macrocyclizations on a solid support using the Heck reaction. 

The polymerization via zwitterions represents a special case of a polymerization with participation by ion pairs. The ion pairs can occur either as intramolecular macrocyclics or as chainlike associates ... 

This has obvious implications in the synthesis of extended nanotube structures. Most recently, Itami reported the selective syntheses of [9]CPP, [10]CPP, [11]CPP, and [13]CPP using modifications of previously reported methods [45]. This is notable in that it contains the first example of intramolecular macrocyclizations to offer [9]CPP, [IIJCPP, and [13JCPP precursors (Fig. 36). 

TPPDS = triphenylphosphine disulfonic acid disodium salt Scheme 3.38 Solid-phase intramolecular macrocyclization. 

A highly convergent synthesis of rutamydn B, a 26-membered lactone macrolide antibiotic has been achieved by intramolecular macrocyclization through Suzuki coupling of a linear alkenyl boronate with a terminal alkenyl iodide as the key step in high yield as reported by White et al. (Scheme 3.68) [103]. 

Scheme 3.68 Intramolecular macrocyclization via Suzuki-Miyaura coupling.

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