Poly cyclization

Scheme 1.11. Cationic domino poly-cyclization for the synthesis of 3-deoxyschweinfurthin B (1-42).

As shown in the preceding examples, although intramolecular Pd-catalyzed poly-cyclization is a well-established procedure, some few examples exist of polycycliza-tions where the first step is an intermolecular process. In this respect, the Pd°-cata-lyzed domino reaction of allenes in the presences of iodobenzene reported by Tanaka and coworkers [40] is an intriguing transformation. As an example the Pd-catalyzed reaction of 6/1-60 in the presence of iodobenzene led to 6/1-61 in 49% yield, allowing the formation of three rings in one sequence (Scheme 6/1.14). 

Table 5.6.1 Potential combinations for (poly) cyclization-anion capture processes...

Using more simple systems, McDonald and Towne were able to demonstrate that pyridi-nium chlorochromate (PCC) is a suitable reagent for carrying out 5yn-oxidative poly-cyclizations (Scheme 3). [6] Thus, transformation of the (Z)-hydroxydiene 14 yielded the bis-tetrahydrofurans 15 and 16. Starting with the ( )-hydroxydiene 17, the bis-tetrahydrofurans 18 and 19 were obtained. 

Cationic monomers are used to enhance adsorption on waste soHds and faciHtate flocculation (31). One of the first used in water treatment processes (10) is obtained by the cyclization of dimethyldiallylammonium chloride in 60—70 wt % aqueous solution (43) (see Water). Another cationic water-soluble polymer, poly(dimethylarnine-fi9-epichlorohydrin) (11), prepared by the step-growth... 

Amino Alcohols. Reaction of chloroformate is much more rapid at the amino group than at the hydroxyl group (4—8). Thus the hydroxy carbamates, which can be cyclized with base to yield 2-oxazoHdones, can be selectively prepared (29). Nonionic detergents may be prepared from poly[(ethylene glycol) bis(chloroformates)] and long-chain tertiary amino alcohols (30). 

Alkanes, dipurin-8-yl-synthesis, 5, 574 Alkanes, poly-N-pyrazoIyl-synthesis, 5, 320 Alkanoic acids, tetrazolyl-anti-inflammatory activity, 5, 835 Alkanoic acids, 4-thienyi-cyclization, 4, 905-906 Alkene metathesis mechanism, 1, 668 Alkenes activated... 

Cyclization of 2-benzyloxybenzoic acid (66) by means of poly-phosphoric acid affords the dibenzoxepinone, 67. Condensation with the Grignard reagent from 3-dimethylaminopropyl chloride, followed by dehydration of the alcohol thus produced affords doxepin (68), presumably as a mixture of geometrical isomers. 

Marvel et al. described [41] the polymerization of 5,6-dibromocyclohexa-1,3-diene (16) to poly(5,6-dibromo-l,4-cyclohcx-2-ene) 17 followed by a thermally induced, solid state elimination of HBr on the formation of PPP 1. The products, however, display some indications for several types of structural defects (incomplete cyclization, crosslinking). 

Polymeranalogous reactions considered above may be referred to as intramolecular condensation transformations since they are accompanied by elimination of low-molecular products. On the other hand, PCSs can be obtained via polymeranalogous transformations, principally intramolecular polymerization reactions . Thermal and chemical cyclization of poly(acrilonitrile) (PAN) is an example of processes of this type. It was demonstrated by a number of researchers216-225 that thermal transformations of PAN follow the scheme ... 

Poly(arylene ether ketone)s can also be modified by introducing the functional groups using similar approaches to polysulfones. For example, poly(arylene ether ketone)s were sulfonated.189 In addition, o-dibenzoylbenzene moieties in the poly(arylene ether)s can be transformed to heterocycles by cyclization with small molecules. These polymers can react with hydrazine monohydrate in the presence of a mild acid in chlorobenzene or with benzylamine in a basic medium.190 Another example of the use of the o-benzyl cyclization strategy is the intramolecular ring closure of poly(arylene ketone)s containing 2,2/-dibenzoylbiphenyl units to form poly(arylene ether phenanthrenes).191... 

Recently, Tour et al. [32] described attempts to prepare PPP derivatives via a Bergman cyclization, starting from substituted enediynes, e.g. poly(2-phenyl-1,4-phenylene) (18) from l-phenyl-hex-3-en-l,5-diyne or the structurally related poly(2-phenyl-1,4-naphthalene) (19) from l-phenylethynyl-2-ethynylbenzene. 

Quite often in the ring-opening polymerization, the polymer is only the kinetic product and later is transformed to thermodynamically stable cycles. The cationic polymerization of ethylene oxide leads to a mixture of poly(ethylene oxide) and 1,4-dioxane. In the presence of a cationic initiator poly(ethylene oxide) can be almost quantitatively transformed to this cyclic dimer. On the other hand, anionic polymerization is not accompanied by cyclization due to the lower affinity of the alkoxide anion towards linear ethers only strained (and more electrophilic) monomers can react with the anion. 

The films were then thermally cycled at tOO, 200 and 300°C for an hour at each temperature in a forced air convection oven to complete the cyclization. The solution imidization procedure has been further described by Summers, et. al. (42,43). A representative structure for the poly(imide siloxane) copolymers is depicted in Figure 5. 

Frequently B will also undergo a back hydrogen transfer which regenerates the parent ketone, as well as cyclization (in most cases a minor reaction) as a result of this competition the quantum yields of fragmentation are typically in the 0.1-0.5 range in non-polar media. When the Norrish Type II process takes place in a polymer it can result in the cleavage of the polymer backbone. Poly(phenyl vinyl ketone) has frequently been used as a model polymer in which this reaction is resonsible for its photodegradation, reaction 2. 

Roush and coworkers developed a new one-pot sequence consisting of an intramolecular Diels-Alder- and an intramolecular vinylogous Morita-Baylis-Hillman-cyclization for the synthesis of spinosyns [31]. These compounds are poly-ketide natural products possessing extraordinary insecticidal activity. 

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