Troponoid systems

Irradiation of troponoid systems leads to a variety of photochemical reactions which include valence tautomerization, deep-seated rearrangement and dimerization. The photochemical transformations of troponoid systems as a general rule proceed readily in Pyrex vessels and thus must involve excitation of the intense, long wavelength absorption band (320-350 m/t) of the troponoid system. 

The recognition, isolation, and characterization of troponoid systems have been facilitated by certain chemical properties (55CRV9 68MI2 73CRV293, p. 354 78MI1 84MI2, pp. 93 and 113), which usually occur in both monocyclic and fused derivatives. 

The troponoid system is included in many natural products, including alkaloids and antibiotics. Therefore, its discovery attracted immediate pharmacological interest. 

The cycloheptatriene ring system is of great interest as a subject for excited state reactions induced by both thermal and photochemical excitation. Major contributions to the photochemistry of the troponoid system and subsequently, to the photochemistry of the cycloheptatriene system have been made by Chapman b whose pioneering work in this field has stimulated much interest in photochemistry in general. The photochemistry of the troponoid system has been reviewed quite thoroughly 1>, and mention will be made only of recent developments in this area. Dimerization reactions will not be discussed. 

As indicated in the Introduction, the photochemistry of tropones proceeds via three different modes, called A, B, and C, with type C occurring in complex polycyclic troponoids. Mukai and Miyashi 72> have observed the first example of a photoreaction of a simple troponoid system to undergo the type C isomerization. Irradiation of 5-phenyltropolone methyl ether (104) in methanol yielded 3-methoxy-6-phenyl-A3>6-bicyclo-[3.2.0]heptadien-2-one (105). The effect of the substituent is important,... 

When a solution of colchicine is exposed to light in the absence of air, three products are isolated in varying amounts, depending on the conditions a-, j8-, and y-lumicolchicine. One feature they all share is the absence of the long wavelength UV-band associated with the troponoid system. A discussion of earlier work on these photoisomers may be found in volume VI. 

Addition to troponoid systems 17, 764 Addition-halogenation 16, 576 Adiponitrile as reagent 17, 577 Air s. Oxygen Alanes (s. a. Aluminum compounds, organo-, Halogenalanes)... 

The examples shown in Scheme 2 illustrate (a) a method for RsC— Br -> RzO or R3C—OH and (b) dialkyladve enone transposition as shown in essence in equation (2). The sequence R2CH—Cl R2CH—Sn -> R20 was crucial in a synthesis of the troponoid nezukone (1), as other methods of functionalizing the R2CH—Cl system in this ring failed (equation 3). The dialkylative enone transposition (equation 2) was illustrated by a short synthesis of dihydrojasmone (equation 4). ... 

In the case of (8aS)-(+)-l,8a-dihydroazulene 10,15 the composition of the apparent CD and UV bands was rather simple, because each of the apparent bands was composed of a single electronic transition. The case of chiral troponoid spiro compounds (15aS)-(-)-14 and (18a5)-(-)-15 was also simple because of their Ci symmetrical structures. 16 On the other hand, the Ji-electron chromophores of the twisted naphthalene-diene systems 22-26 are complex and have no symmetric character.18 Therefore, to clarify the applicability of the 7i-electron SCF-CI-DV MO method to such complicated systems, it is important to analyze the composition of the apparent CD and UV bands theoretically obtained. As illustrated in Figure... 

Fulvenes, like their troponoid counterparts, are capable of engaging dienes in a number of different pericyclic reactions. A reasonably well-defined reactivity profile of these systems has emerged as the result of extensive scrutiny of the cycloaddition behavior of the fulvene nucleus. To a large extent, fulvenes undergo concerted cycloadditions to dienes as either the 6ir or 2ir participant and the factors governing which of these reactivities is expressed in a particular circumstance has been elucidated employing frontier molecular orbital considerations. ... 

From azulenes by annulation onto the hve-membered ring 2.3.5.7 From 1-haloazulenes. The use of functionalized azulenes, especially halo and amino derivatives (Sections 2.3.5.1-2.3.5.5), is regarded to be the most universal approach to polycyclic systems based on azulene (82JOU132). Many of the precursors for their part are readily accessible from active troponoids (04EJO899). 

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