Chromium electron-deficient diene complexes

Irradiation of a solution of thiepine 1,1-dioxide chromium complex (15) in the presence of diene (99), followed by metal decomplexation with oxygen provided [6 -I- 4] cycloadducts (100) <92TL5873, 93JA1382). The relative stereochemistry of the products (100) was shown to be derived from an endo transition state. The electronic character of the diene (99) appears to offer a moderate influence on reaction efficiency. For example, yields were uniformly lower for reactions involving electron-deficient diene partners relative to those employing electron-rich dienes (Equation (17)). 

Higher-order Cycloaddition Reactions. By far, the most extensively investigated reaction of chromium complex 1 is the [6 + 4 ] cycloaddition reaction. The reaction between complex 1 and several dienes was examined, and it was determined that electron-rich 4 partners provided much higher yields than those of electron deficient partners. Thus, diene 14 reacts with chromium complex 1 under photochemical conditions to give an excellent yield of cycloadduct 15, whereas, diene 16 gives a 38% yield of the corresponding cycloadduct 17 (eq 5). ... 

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