... both the dienophile and the other N-CH2Ar group. In the transition state, the formyl hydrogen atom is placed in proximity to the oxy-gen substituent on the boron atom, and held there by a ... K, caused by forma-tion of a charge-transfer complex between the p-donor indole ring and the accep-tor aldehyde. The intermediate is thought to be as shown in Fig. 1.2, in which the s-cis conformer ... 1,4-benzoquinone in 1920. This research laid the ground work forDiels and Alder. The basis of the Diels-Alder reaction developed in the twenties, and the contri-bution by Woodward and Hoffmann in the...