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The [4+2] cycloaddition of ortho-boronoanilide dienophile 4 with cyclopentadiene was found to proceed faster than both its para isomer 8 and the unsubstituted derivative 6, thereby confirming that self-activation by internal coordination is operative in the case of 4. Chiral boronic esters derivatives 9 and 10 provided a small level of remote 1,8-stereoinduction. These results show that dialkoxyboronic esters can operate as weak, internal Lewis acids and activate carbonyl-containing functionalities in cycloaddition reactions.
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Kennedy et al. (2002) studied this question.
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