Reactions List-Barbas-Mannich

Hayashi Y, Tsuboi W, Shoji M, Suzuki N (2003a) Application of high pressure induced by water-freezing to the direct catalytic asymmetric three-component List-Barbas-Mannich reaction. J Am Chem Soc 125 11208-11209... 

In the same year Hayashi [20] reported a very successful high-pressure, induced by water-freezing, direct asymmetric three-component List-Barbas-Mannich reaction catalyzed by L-proUne. One year later Hayashi used a similar approach for the aldol reaction (Scheme 21.4) [22]. The use of ca. 2 kbar pressure at -20 °C for the L-proUne catalyzed aldol reaction between benzaldehyde and acetone (27 equiv) in DMSO gave the product in 78% yield and 75% ee. The control experiment at-20 °C and atmospheric pressure provided the aldol product with considerably lower yield (40%) and similar enantioselectivity. 

List B, Lerner RA, Barbas CF 3rd (2000) Proline-catalyzed direct asymmetric aldol reactions. J Am Chem Soc 122 2395-2396 List B, Pojarliev P, Martin HJ (2001) Efficient proline-catalyzed Michael additions of unmodified ketones to nitro olefins. Org Lett 3 2423-2425 List B, Pojarliev P, Biller WT, Martin HJ (2002) The proline-catalyzed direct asymmetric three-component Mannich reaction scope, optimization, and application to the highly enantioselective synthesis of 1,2-amino alcohols. J Am Chem Soc 124 827-833... 

In the early 1970s, i-proline (222) was shown to function as a chiral catalyst for enantioselective aldol addition reactions (Chapter 4) [156]. With the aim of expanding the scope of proline-catalyzed asymmetric aldol additions [157], List reported that proline also catalyzes enantioselective Mannich reactions (Equation 19) [158]. Whereas most catalytic enantioselective Mannich reactions with aldehydes typically afford the corresponding syn products, Barbas, Tanaka, and Houk demonstrated that the complementary anti products such as 232 could be obtained highly selectively in the presence of the methyl-substituted proline catalyst 229 (99% ee, 98 2 dr. Scheme 11.33) [159]. It was proposed that these transformations proceeded through the energetically favored enamine 230 and transition state structure 231. 

Surprisingly, little follow-up work on this idea of small molecule asymmetric catalysis appeared for the next 25 years. In the late 1980s, Agami reported the asymmetric intramolecular aldol reaction of acyclic diketones with (S)-proline as the catalyst. It was not nntil the twenty-first centnry, however, when this notion of organocatalysts became fnlly exploited. List and Barbas ° pioneered enam-ines as catalysts for aldol and Mannich and related reactions. MacMillan has developed a variety of imininm-based catalysts prodncing large asymmetric indnction for Diels-Alder chemistry, Friedel-Crafts alkylations, Mnkaiyama-Michael and cyclopropanation " reactions. 

List B. Asymmetric aminocatalysis. Synlett 2001 1675-1686. Notz W, Tanaka F, Barbas III CF. Enamine-based organocatalysis with proline and diamines the development of direct catalytic asymmetric aldol, Mannich, Michael, and Diels-Alder reactions. Acc. Chem. Res. 2004 37 580-591. 

The scope of this chapter does not allow nor attempt a comprehensive account of all developed processes to date. A detailed summary, in particular of aldol, Mannich, or ot-functionalisation reactions, can be found in excellent reviews written on the topic." Barbas and List reported an asymmetric, direct, intermolecular aldol reaction of acetones and aldehydes (Scheme 5.4), presumably via enamine formation of proline and acetone. As compared to its metal-catalysed alternatives, no preformation of the respective enolate is required, a mode of action that mimics metal-free aldolase enzymes. ... 

Not long after List published his three-component methodology, the group of Barbas reported a fairly similar procedure [3]. Besides L-proUne (1), a penicillamine derivative appeared to effectively catalyze the reaction. Later on, various ketone donors 7b, 7e-g were successfully subjected to the preformed iV-PMP-protected a-imino ethyl glyoxylate 10a as imine acceptor, thereby yielding y-oxo-a-amino acid derivatives lla-d as the products (Scheme 5.4). Analogous to the results of List, the reactions proceeded smoothly resulting in Mannich products with excellent yn-selectivity in complete enantiomerically pure form [4],... 

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