Quinone dimethide

Wang, J. Pettus, L. H. Pettus, T. R. R. Cycloadditions of o-quinone dimethides with p-quinol derivatives regiocontrolled formation of anthracyclic ring systems. Tetrahedron Lett. 2004, 45, 1793-1796. 

FIGURE 6.42 Oxidation of 3-oxa-chromanol 58 in the presence of 1 equivalent of water mechanistic study hy means of selectively deuterated starting material. The initially formed ortho-quinone dimethide 63 rearranges into styrene derivative 64, which then reacts with water to provide acetophenone 61. 

Benzocyclobutene reacts with a range of heterodienophiles under mild conditions through the intermediacy of an o-quinone dimethide the reaction with aldehydes gives high yields of... 

The //////-substituted benzocyclobutenes 601 undergo bond reorganization under mild conditions to form ortho-quinone dimethide intermediates 602, which function as dienes in an hDA reaction with aldehydes to afford all syn-substituted isochromans 603 in excellent yield (Scheme 129) <2000AGE1937>. 

As depicted in Scheme 41, an intramolecular cycloaddition of the furan 2,3-double bond of a furan tethered to a cyano-substituted benzocyclobutene via an intermediate quinone dimethide was used for the synthesis of the tetracyclic core of halenaquinol and halenaquinone <2001SL1123, 2002T6097>. The reaction proceeded via an OT,7i9-transition state to produce the cycloadduct 72 exclusively. A related chemistry is shown in Equation (56), in... 

The utility of 141 was emphasized by a recent synthesis of idarubicinone (9) [146] (Scheme 30). Cycloaddition of quinone 143, prepared from 141 by ketalization and cerimn ammonimn nitrate (CAN) oxidation [20], with a novel precursor of o-quinone dimethide [146], tran -, 2-bis(trimethylsilyloxy)benzocyclobutane (142), and subsequent removal of protecting groups gave idarubicinone (9) in 65% overall yield. 

Most of the azulenoheterocycles having the azuleno-o-quinone dimethide structure (type 3) are less stable than the other types (87H(26)2025). o-Quinonoid azulenothiophene 44 is rather unstable even at room temperature and could not be demethoxycarbonylated (83CL1721). o-Quinonoid furan 168 is not isolable at all (83CC1025). Furans 149 (rather unstable) and 152 show bond fixation, they are more stable than isobenzofuran, but behave similarly with respect to Diels-Alder cycloaddition (03OBC2383). 

Several research groups have studied synthetic approaches based on cycloaddition of quinone dimethides to bicyclic quinones (disconnection c in 98). In our laboratories we have prepared the quinone 123 in which the full ring A... 

Both thermal and photochemical rearrangement of (667) affords (668) and (669). Conversion of (667) into (669) may be regarded as a bishomo analogue of the o-quinone-dimethide-benzocyclobutene rearrangement. ... 

A plausible explanation for the observed regiochemical outcome may involve preliminary transformation of the putative laterally hthiated aryltetrahydrofuran 125 into the reactive o-quinone dimethide alkoxide derivative 126 (2011AGE6906). This 1,4-elimination product 126 may then undergo a nucleophilic conjugate addition by a second equivalent of base to give the tertiary benzylic carbanion 127. This is finally intercepted by the electrophile (if any) to furnish adduct 128 after acid quenching at room temperature (Scheme 35). 

The formation and subsequent [4 + 4] cycloaddition of pendant benzo-quinone dimethide species was utilized by Hawker and coworkers in the synthesis of architecturally defined SCNPs (Figure 4.2). Statistical copolymers of 4-vinylbenzocyclobutene were synthesized by nitroxide-mediated free radical polymerization. The nanoparticle synthesis employed a continuous addition strategy, in which a concentrated polymer solution... 

As mentioned earlier, o-quinone dimethides such as l,6-monocyclic(4]dendralene 134 are both linear and cross-conjugated, and thus fall outside the scope of this review. In our view, this connectivity pattern only corresponds to a dendralene when the ring system contains more than six carbon atoms. 

Benzocyclpbutenes. When benzocyclobutenol is heated, it is converted into o-methylbenzaldehyde, If the reaction is done in the presence of a dienophile such as dimethyl acetylenedicarboxylate, an adduct (350) is formed. These observations suggest that the hydroxy-o-quinone dimethide (349) is the initial... 

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