Regio- and enantioselective substitution of primary endocyclic allylic sulfoximines with organocopper and organocuprate reagents. The importance of iodide for the allylic substitution with organocopper compounds

Article abstract of DOI:10.1021/ja00114a009

The endocyclic N-substituted allylic sulfoximines 17-20 and 26 were synthesized from the corresponding cycloalkanones and the various (S)-5-(lithiomethyl)-S-phenylsulfoximines in enantiomerically pure form in yields of 60-70% in a process involving the isomerization of the intermediate vinylic sulfoximines. Desilylation of 26 gave the parent N-H sulfoximine 27 from which the N-sulfonylsulfoximines 28 and 29 were prepared. The X-ray crystal structure of 28 was determined. The allylic sulfoximines 17-20 and 26-29 did not racemize or rearrange thermally to the corresponding allylic sulfinamides. Reaction of the allylic sulfoximines 18, 28, and 29 with the organocuprate reagents 2/LiI, 35/LiI, and 47/LiI led with α-selectivities of 92:8 to 99:1 to the endocyclic alkenes 39 in good to high yields. Reaction of 17-20, 28, and 29 with the organocopper reagents 5/LiI, 30/LiI, 31/LiI, 32/LiI, 33/LiI, 34/LiI, and 37/LiI in the presence of BF₃ resulted in the formation of the exocyclic alkenes 38, 41, 43, and 45, respectively, in good to high yields with γ-selectivities of 80:20 to 99:1. The sulfonimidoyl group imparts asymmetric induction to the substitution in the range of 27-90% ee. The (S)-sulfonimidoyl group leads to a preferential bond formation from the si side of the double bond. From the sulfoximines 18 and 26-29 the N-methylsulfoximine 18 and the N-tosylsulfoximine 28 showed the highest and lowest reactivity with the butylcopper reagent 32/LiI in the presence of BF₃, respectively, while in the absence of BF₃ only 29 reacted. The Lewis acid most likely serves to activate the N-methyl- and N-tosylsulfoximines or intermediates thereof through coordination at the sulfonimidoyl and sulfonyl group. Reaction of the sulfoximines 18 and 29 with pure Me₃SiCH₂Cu (34) revealed a strong rate acceleration by LiI and an even stronger one by Bu₄NI. This points to the existence of a heteroleptic cuprate or a related compound as reactive species. In substitutions with the Yamamoto reagents RCu/MX/BF₃, the halide is important and a reaction between RCu and BF₃ does not have, at least in the case of allylic sulfoximines, to be invoked. In reactions of 17-20 besides the alkenes, the sulfinamide ent-4 was formed with an ee value of 97% in high yield with retention of configuration. The absolute configuration of the exocyclic alkenes 38, 41, and 45 was determined by ozonolysis to the corresponding cycloalkanones followed by their conversion to the corresponding lactones and/or CD measurement of the former.