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Metal-Promoted Higher-Order Cycloaddition Reactions.Stereochemical, Regiochemical, and Mechanistic Aspects of the (6π + 4π) Reaction.-Chromium complexes, e.g. (I), (VI), (VIII) and (XI), undergo photochemically initiated (6 + 4) cycloadditions with electron-rich and electron-deficient dienes to give endo cycloadducts such as (III), (V), (VII), (IX), (X) and (XII). Little regioselectivity is observed for 2-or 3-substituted cycloheptatriene complexes, e.g. (VIIIc)-( VIIIe). In the case of (VIII) reaction conditions are improved by CO treatment of the photolysis products. The (6 + 4) cycloadditions can also be effected thermally. When molybdenum or tungsten complexes are used the cycloadditions proceed less efficiently. -(RIGBY, J. H.; ATEEQ, H. S.; CHARLES, N. R.; CUISIAT, S. V.; FERGUSON, M. D.; HENSHILWOOD, J. A.; KRUEGER, A. C.; OGBU, C. O.; SHORT, K. M.; HEEG, M. J.; J.

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