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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 – 13 provided a small level of remote 1,8-stereoinduction transmitted through a putative tetrahedral stereogenic boronate complex. 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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