Cyclization Studies

In the case of amino acid ester and amide complexes, the intramolecular hydrolysis reaction was not observed directly, but was deduced from the results of lsO tracer studies. However, recently the cis-hydroxo and cis-aqua complexes derived from the bis(ethylenediamine)cobalt(III) system, containing glycinamide, glycylglycine and isopropylglycylglycinate, have been isolated and their subsequent cyclization studied over the pH range 0-14.160,161... 

This analysis was confirmed by the cyclization studies of hydroxyketone thiols 69 and 72. Compound 69 gave on cyclization the isomer 70 rather than the isomer 71 which has an equatorial oxygen. Similarly, cyclization of 72 gave 73 only the isomer 74 was not observed. It was further shown that compounds 70 and 73 exist in a conformation equivalent to 68A, which has two anomeric effects. 

Cyclization studies have also been carried out on the chemical copolymers poly (ethylene, dimethylsiloxane), and poly(styrene, dimethylsiloxane).68,69 99 Numerous intramolecular interactions need to be taken into account in a chemical copolymer and,... 

Earlier syntheses of arylquinolizidine alkaloids mainly utilized the pelletierine condensation to construct the basic skeleton, 4-aryl-2-quinolizidinone (11) (Scheme 1). Two mechanistic pathways, involving (a) initial aldol condensation of pelletierine (8) with an aromatic aldehyde followed by intramolecular Michael-type addition of the resulting enone 9 (6, 7) and (b) a Mannich-type reaction through 10 (8, 9), were proposed without any experimental evidence. Preparation and cyclization studies of the intermediate 9, however, gave conclusive evidence to show that the pelletierine condensation proceeded through pathway a (10). 

Palladium-catalyzed cyclization of the oxime derivative 47 provided a good yield of the pyrrole 48 (Equation 9) <1999CL45>. Similar reactions have been observed in connection with cyclization studies of related ketone trimethylhydrazonium salts <2005H(65)273>. Photochemical radical cyclization of 7,5-unsaturated ketone oximes has been reported to produce 1-pyrrolines <2005TL2373>. Similar 0-acetyloximes may also be annulated to 1-pyrrolines by treatment with acetic acid in the presence of 1,4-cyclohexadiene and naphthalene-l,5-diol, possibly proceeding via a radical mechanism <2002CL144>. 

A similar strategy has been applied to the synthesis of kainoids and related compounds (eq 3). Both stoichiometric and catalytic amounts of cobalt reagents have been used in these and other cyclization studies. Several examples of these types of cyclizations have been published, including cyclizations using aryl halides as precursors to aryl radicals. ... 

Previous observations on the high reactivity of (benzoxazol-2-yl) thioesters toward various aminest prompted the development of uronium salts HSBTU (ll)t l as well as HATTU (13) and HAPyTU (29).t 9 However, HATTU and HAPyTU were less reactive and provoked more epimerization in both cyclization studies and fragment condensations than the corresponding oxygen analogues HATU (12) and HAPyU (28).f 9... 

An example of several PPA cyclizations studied by Koo - " is the preparation of ethyl 6,7-dimethoxy-3-methylindene-2-carboxylate (13). The keto ester (12) is added to PPA precooled to 5° in a beaker, and the mixture is stirred thoroughly... 

Further transannular cyclization studies start from (E)- or(Z)-5-cyclodecenone while radical-induced reactions form hydroazulene skeletons predominantly, the acid-catalyzed reactions generate hydronaphthalene systems. Only 1,6-cyclization products are observed, the L -config-urated cyclodecenone leads to the tram, while the Z-configurated material yields the cis ring... 

Cyclization studies were carried out in sealed tubes in toluene solutions at 165 °C and provided excellent yields of the corresponding bicyclic cycloadducts in 5-9 h. Reactions of tertiary alkyl ethers showed moderate to complete trans selectivity. This selectivity was observed even for inherently cw-directing systems and may be attributed to the gem-dimethyl group in the ether tether comparison of the reacting conformations leading to cis- and rrans-fused decalins reveals, in the cis case, an unfavorable non-bonding interaction between the axial methyl group and H-C(3) of the diene (Scheme 10-15). 

To obtain sufficient quantities of the indole 83 for their cyclization studies, an improved synthesis of this key intermediate via an alternate route was developed (Scheme 24). 

Vicinal diynes have been prepared as intermediates for subsequent cyclization studies (Scheme 87). Monoprotected acetylene was used. Coupling with 2,3-dichloroquinoxaline gave the dialkyne 232. The vicinal pair in the pyridine 233 was a bromo and a triflyloxy substituent, and in the pyrimidine 234 a chloro and an iodo substituent. The dialkynylated products were obtained in modest to good yields. ... 

Another reaction that has been extensively studied is the y-lactam formation. The initial cyclization study using a secondary amide tether did not afford any desired product. It was believed that the predominant trans conformation of the secondary amide prevented the cyclization (Figure 2-16). In fact, the protected enynes with a tertiary amide linked were readily transformed into a variety of y-lactams. Under the optimized conditions, enyne-amide 475 afforded functionalized y-lactams 476 in high yield and good-excellent enantioselectivities... 

In an examination of the tendency to form catenanes, a series of 3,4-dimethoxy-2,6-pentacosamethylenephenylaminobis(alkyl chains did not lead to catenane precursors. ... 

Cyclization studies have also been carried out on the chemical copolymers poly(ethylene, dimethylsiloxane) and poly(styrene, dimethylsilox-ane). Numerous intramolecular interactions need to be taken into account in a chemical copolymer. Consequently, the results on the copolymers have been given only a preliminary interpretation in terms of rotational isomeric state theory. Cyclization calculations have also been carried out for poly(dihydrogensiloxane) [-SiH O-], but at present there are no experimental data available for comparison with theory. 

The concept of folding-strain stereo-control has been developed to explain diastereo-facial selection in ring-closure reactions. The cyclizations studied were of two types of substrate, with substituents at various points on the acyclic chains 2-(6 -trimethylsilylhex-4 -enyl)cyclohexen-2-ones and ethyl 7-bromo-2-methylhexanoates. 

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