Alkylation of allylic derivatives. 4. On the mechanism of alkylation of allylic N-phenylcarbamates with lithium dialkylcuprates

Abstract

Acknowledgment. We express our appreciation to Dr. U. Weiss for valuable discussions.Registry No. (S)-(-)-2a, 65915-63-1; (S)-(-)-2b, 84580-10-9;(S)-(-)-3, 84499-95-6; (±)-4a, 79605-67-7; (S)-(-)-4a, 84580-11-0; (S)-(-)-4a camphanate, 84520-47-8; (S)-(-)-4b, 78341-38-5; 5, 6786-30-7; (S)-(-)-6a, 84499-96-7; (S)-(-)-6b, 84499-97-8; (S)-(-)-7, 55095-00-6; 8, 829-14-1; (S)-(-)-9a, 84499-98-9; (S)-(-)-9b, 84499-99-0; (fi)-(+)-10,84500-00-5; (S)-(-)-10,84500-01-6; (±)-lla, 62249-35-8; (fi)-(-)-lla, 62210-83-7; (fi)-H-lla camphanate, 84580-12-1; (R)-(-)-llb, 84580-13-2; benzocyclohepten-3-one, 826-73-3.

Copper‐mediated Diastereoselective Conjugate Addition and Allylic Substitution Reactions

“…Employing the enantiomerically enriched carbamate (R)-163 (82% ee) as the starting material, the proposed syn-attack of the organocopper nucleophile could then be as shown. Thus, after substitution and subsequent hydrogenation, (R)-2-phenylpentane (169) was obtained in 64% ee [75]. Scheme 6.35.…”

“…Suitable leaving groups have been found in carbamates [74,75], (O/S)-benzothiazoles [76,77] (Scheme 6.32) and, very recently, the ortho-diphenylphosphinobenzoyl (o-DPPB)-group was identified as an efficient reagent-directing leaving group (Scheme 6.44) [91]. Scheme 6.32.…”

“…Results of allylic substitution of styrene system 163 with organocopper reagents. Better results were obtained for the carbamate of 163 (entry 3) [75,80]. Thus, deprotonation of the carbamate 163 with a lithium base, followed by complexation with copper iodide and treatment with one equivalent of an alkyllithium, provided exclusive g-alkylation.…”

Enantioselective Iridium‐Catalyzed Allylic Arylation

“…In this case, however, the ratio of products 2 a/3 a and the conversion of the reaction were lower than that for 1 a. Unfortunately, neither a phosphonate (1 ad, Table 2, entry 4), nor a carbamate (1 ae, Table 2, entry 5) [28] were able to improve the results obtained with 1 a. We therefore selected the carbonate leaving group for further studies as it is the best compromise between efficiency and reactivity.…”

Pharmaceuticals

“…The reaction of the hydroxy-function with phenyl isocyanate generates a protecting group, which also serves as a leaving group for the next but one step. The catalytic dihydroxylation occurs selectively at the terminal double bond; the carbamate can then be displaced in a syn-facial S N 2' reaction [102] by a silyl residue, without significant loss of enantiomeric purity. Oxidative cleavage of the diol and reductive amination with dibenzosuberylamine (DBS-NH2) gives the first central building block in this convergent synthesis, and appears ultimately as ring C of the morphine skeleton.…”