Fe(II)-catalyzed imidation of allyl sulfides and subsequent [2,3]-sigmatropic rearrangement. Preparation of alpha-branched N-tert-butyloxycarbonyl (Boc)-protected N-Allylamines

Allyl aryl sulfides 1 and 5 were shown to undergo an imidation/[2,3]-sigmat ropic rearrangement reaction upon treatment with N-tert-butyloxycarbonyl az ide (BocN(3)) and catalytic amounts of FeCl2 in CH2Cl2. The N-Boc-protected N-allyl sulfenamides 3 and 21 were obtained in yields between 48 and 75% ( 12 examples), Whereas the reaction is well suited for the transformation of alpha-unbranched sulfides to a-branched sulfenamides, the enantiomerically pure alpha-branched sulfides 10 and 13 reacted sluggishly. The correspondi ng sulfenamides 22 and 23 were obtained in only moderate enantiomeric exces s (36-39% eel. A reaction mechanism is proposed that postulates the interme diacy of an N-Boc-substituted Fe(IV)-nitrene complex 14 acting as the imida tion reagent in the catalytic cycle. Possible side reactions are discussed. The benzenesulfenamides 3 were further converted into N-Boc-N-allylamines 4 by removal of the phenylsulfanyl group. Bu3SnH in benzene was found to be the reagent of choice for the deprotection of alpha-branched amines that b ear a secondary allyl substituent (five examples, 71-93% yield). This metho d failed for the alpha-branched amines 3i-k with a tertiary allyl substitue nt. The phenylsulfanyl group was finally removed with P(OEt)(3)/NEt3 in CH2 Cl2 (three examples, 43-62% yield).