Formation and Reactivity of 2-Styryl-1,4-benzoquinones
摘要:
The 2-styryl-1,4-benzoquinones 7a,b, generated by the oxidation of the corresponding hydroquinones 6a,b, dimerize at room temperature in a Diels-Alder reaction. The strictly chemo, regio- and stereoselective process can be rationalized by means of frontier orbital interactions, The polycyclic adducts 8a,b undergo a further intramolecular cycloaddition (8a,b --> 10a,b) after oxidation on silica gel.
Formation and Reactivity of 2-Styryl-1,4-benzoquinones
摘要:
The 2-styryl-1,4-benzoquinones 7a,b, generated by the oxidation of the corresponding hydroquinones 6a,b, dimerize at room temperature in a Diels-Alder reaction. The strictly chemo, regio- and stereoselective process can be rationalized by means of frontier orbital interactions, The polycyclic adducts 8a,b undergo a further intramolecular cycloaddition (8a,b --> 10a,b) after oxidation on silica gel.
2-Styryl-1,4-benzoquinone (1) and compounds 2 and 3 containing 1 as a substructure all proved to be highly reactive towards thermal or photochemical [4pi + 2pi] cyclodimerization reactions. Chemo-, regio- and stereoselective processes lead to dimers (compounds 1-10), which can undergo secondary reactions consisting of the addition of nucleophiles combined with a twofold keto-enol tautomerism (10 --> 12). An alternative process is dehydrogenation/oxidation followed by an intramolecular [4pi + 2pi] cycloaddition (10 --> 11). The same selective [4pi + 2pi] cyclodimerization can be observed in solution upon irradiation (e.g., 1a --> 10a), in contrast to irradiation in the crystalline state which yields a [2pi + 2pi] dimer (e.g., 1a --> 13). If more than one styrylbenzoquinone moiety is present in the same molecule the oligomers 2a (n = 1-3) and 3a (n = 1-4) are obtained. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).
Formation and Reactivity of 2-Styryl-1,4-benzoquinones
The 2-styryl-1,4-benzoquinones 7a,b, generated by the oxidation of the corresponding hydroquinones 6a,b, dimerize at room temperature in a Diels-Alder reaction. The strictly chemo, regio- and stereoselective process can be rationalized by means of frontier orbital interactions, The polycyclic adducts 8a,b undergo a further intramolecular cycloaddition (8a,b --> 10a,b) after oxidation on silica gel.