- In situ enzymatic screening (ISES): A tool for catalyst discovery and reaction development
-
Can enzymes help organic chemists identify new transition-metal catalysts? The first example of the in situ enzymatic monitoring of an organic transformation is described. Thus, a transition-metal-mediated allylic-amination reaction in the organic layer (
- Berkowitz, David B.,Bose, Mohua,Choi, Sungjo
-
p. 1603 - 1607
(2007/10/03)
-
- Fe(II)-catalyzed imidation of allyl sulfides and subsequent [2,3]- sigmatropic rearrangement. Preparation of α-branched N-tert-butyloxycarbonyl (Boc)-protected N-allylamines
-
Allyl aryl sulfides 1 and 5 were shown to undergo an imidation/[2,3]- sigmatropic rearrangement reaction upon treatment with N-tert- butyloxycarbonyl azide (BocN3) 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 α-unbranched sulfides to α-branched sulfenamides, the enantiomerically pure α-branched sulfides 10 and 13 reacted sluggishly. The corresponding sulfenamides 22 and 23 were obtained in only moderate enantiomeric excess (36-39% ee). A reaction mechanism is proposed that postulates the intermediacy of an N-Boc-substituted Fe(IV)-nitrene complex 14 acting as the imidation 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 α- branched amines that bear a secondary allyl substituent (five examples, 71- 93% yield). This method failed for the α-branched amines 3i-k with a tertiary allyl substituent. The phenylsulfanyl group was finally removed with P(OEt)3/NEt3 in CH2Cl2 (three examples, 43-62% yield).
- Bach, Thorsten,Koerber, Christina
-
p. 2358 - 2367
(2007/10/03)
-
- Synthesis of unnatural amino acids via suzuki cross-coupling of enantiopure vinyloxazolidine derivatives
-
(R and S)-α-Amino alcohols and α-amino acids, including 4-methoxyhomophenylalanine, with a variety of unnatural side chains have been synthesized via palladium-catalyzed cross-coupling Suzuki reactions. The key building blocks 1 and 2, synthesized from the common achiral precursor 2-butene-1,4-diol, were made enantiopure utilizing a Pseudomonas cepacia lipase-catalyzed kinetic resolution. The optimal conditions for the Suzuki cross-coupling and the subsequent oxidations of the resultant α-amino alcohols are described.
- Sabat, Mark,Johnson, Carl R.
-
p. 1089 - 1091
(2007/10/03)
-