Stereo- and regioselectivity of Pd(0)/InI-mediated allylic additions to aldehydes and ketones. In situ generation of allylindium(III) intermediates from N-acylnitroso Diels-Alder cycloadducts and 1-amino-4-acetoxycyclopentenes.

Abstract

Acylnitroso Diels-Alder cycloadduct (11, 37, and 45)- and cyclopentenyl acetate (8 and 9)-derived allylindium(III) species were generated in situ from palladium(0) catalysts and indium(I) iodide, and the stereo- and regiochemistry of their additions to aldehydes and ketones were investigated. Solvent, catalyst, and ionic effects were examined for the reaction of N-acetyl cycloadduct (11) and benzyloxyacetaldehyde (10). The solvent mixture of THF/H(2)O with Pd(OAc)(2).PPh(3) catalysis was found to be optimal. The addition of N-acetyl cycloadduct to aliphatic aldehydes afforded products in good yields and high regio- and stereoselectivity, with the cis-1,4-isomers constituting 90-95% of the products. The reactions with N-Boc (37a) and N-methylcarbamate (37b) cycloadducts also gave the cis-1,4-products predominantly. The same regio- and stereoselectivity applied to the reactions of 4-acetoxy-1-(N-hydroxyphenyacetamido)cyclopentene (8). 4-Acetoxy-1-phenylacetamidocyclopentene (9), however, afforded trans-1,4-products exclusively. Mechanistic speculations involving chelated transition states are described.