“On water” direct catalytic vinylogous Henry (nitroaldol) reactions of isatins for the efficient synthesis of isoxazole substituted 3-hydroxyindolin-2-ones

The first example of an "on water" direct catalytic vinylogous Henry addition of 3,5-dialkyl-4-nitroisoxazoles to isatins is described, giving products in excellent yields and up to excellent diastereoselectivities. A remarkable rate-enhancement by water was observed under mild conditions. This approach provides a highly efficient and environmentally benign access to medicinally important isoxazole substituted 3-hydroxy-2-oxindole derivatives.