Polycyclic fused

Quinoline derivatives are of major interest as bioactive compounds. A new method for the synthesis of polycyclic fused quinolines 4-207 was developed by Rossi and coworkers [71], who used the [2+2] cycloaddition of an alkyne 4-204 with enamines 4-205 to give 4-206 (Scheme 4.45). Thereby follows an annulation, with the formation of 4-207a-c. 

The di-rc-methane rearrangement is also a convenient way of obtaining polycyclic fused ring systems as illustrated in the synthesis of a tricyclo-undecane (3.17) 327). In the irradiation of dihydrotriquinacene the initial bonding scheme is identical as in (3.14) but ultimate cyclopropane formation is hindered by structural reasons (3.18) 328). 

Catalytic hydrogenation of polycyclic fused nitroso acetals is a more complex reaction sequence. This process was successfully used in the synthesis of natural and biologically active compounds (see, e g., Refs. 148, 367 and the review 99). 

The forward reaction is extremely easy bevause of aromaticity recovery. These aspects of the intramolecular Diels-Alder reaction are generally very useful and able to provide polycyclic fused six-membered ring compounds which are otherwise difficult to realize. The controlling factors, geometry and mechanism of intramolecular Diels-Alder reactions have been comprehensively reviewed elsewhere i°4,106), and it is not our intention to discuss these in details. However, the synthetic utility of the reaction is demonstrated by the following examples107). 

Other procedures for generating chains from polycyclic fused ring systems and for disconnecting fused rings which use simple graph theoretical approaches have been described.35 They make use of the dual of the molecular graph, i.e. the figure... 

Application of Corey s rules to polycyclic fused ring structures. The dual graph procedure... 

To carry out MCRs of aminoazoles with aldehydes and cyclic CH-acids, the methods of green chemistry were also applied. For example, treatments of 3-methylisoxazol-5-amine and aromatic aldehydes with 1,3-cyclohexanedione, dimedone, 1,3-indanedione, or titronic acid were proceeded in water under micro-wave irradiation at 120°C [100] (Scheme 31). As a result, clean, efficient, and convenient procedures for the generation of polycyclic-fused isoxazolo[5,4-b] pyridines 71 were developed. An interesting fact is that, in the case of 1,3-cyclohexanedione, dihydropyridine s were obtained while in aU other cases only hetero-aromatized derivatives were isolated. No reason for this experimental fact was discussed in the article. 

Remarkable syntheses of polycyclic fused systems such as 38 by treatment of simple compounds 37 with base have emerged from Takasu and Ihara.13 You might compare the skeleton of 38 with that of 30. 

These methods for the synthesis of fused ring /3-lactams have been extensively applied to the synthesis of tricyclic or polycyclic fused ring systems and Section 2.04.11 should be consulted for more details. 

This section is devoted to tricyclic and polycyclic fused azetines, azetidines, and azetidinones. Since the publication of CHEC-II(1996), there has been a marked increase in activity in this area and a wide variety of different types of compounds have been studied. Other examples of these compounds are mentioned in CHEC(1984) and CHEC-11(1996), and should be consulted in addition to this section. 

Tu and co-workers [74] have synthesized a series of new polycyclic-fused isoxazolo[5,4-h]pyridines 25-29 by a one-pot tandem reaction under microwave... 

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