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The development of a new class of hydrazide type organocatalyst, (4R,5R)-1,3-bis(isopropylamino)-4,5-dihenylimidazolidin-2-one 2a, for enantioselective Diels-Alder reactions between cyclopentadiene and α,β-unsaturated aldehydes are presented. The new organocatalyst 2a promoted the reaction, affording Diels-Alder adducts in good yields with good levels of enantioselectivity.

Some hydrazines and hydrazides were prepared and screened for their catalytic efficiencies in Diels-Alder reactions. 1 H-NMR studies and ab initio calculations revealed that catalytic efficiencies of these catalysts are greatly dependent on the release of the catalysts from the Diels-Alder adducts. INTRODUCTION In the early 1970s, two industrial research groups reported the first examples of (S)-proline-catalyzed enantioselective intramolecular aldol reactions. These reactions, so-called Hajos-Parrish-Eder-Sauer-Wiechert reactions, attracted little attention for about 30 years despite their potential values. 1 In the early 2000s, List and coworkers reported (S)-proline-catalyzed intermolecular asymmetric aldol reactions. 2 Thereafter, as well as proline, related five-membered cyclic secondary amine derivatives have also been applied to many reactions that proceed through enamine or iminium ion intermediates. 3 It is well established that a nitrogen atom that is directly bonded to an atom with one or more lone pairs, such as H 2 N-NH 2 and H 2 N-OH, tends to be a stronger nucleophile than would otherwise be expected. The nucleophic enhancement is called "α-heteroatom effect", 4 and such α-nucleophiles seem to be more advantageous as nitrogen-based heterocyclic organocatalysts than simple secondary amine catalysts, but there are not many reported examples. This type of organocatalyst was first reported to promote Diels-Alder reactions efficiently via iminium ions in 2003, 5 and camphor-based chiral hydrazide catalysts were also reported. 6 Recently, we have investigated Biginelli reaction catalyzed by cyclic hydrazine-type organocatalysts as shown in Figure 1, and we have reported that pyrazolidine dihydrochloride 1a could catalyze Biginelli reactions very efficiently under mild conditions. 7 These results promoted us to screen several cyclic hydrazines and hydrazides for their catalytic activities

A Novel Hydrazide Type Organocatalyst for Enantioselective Diels-Alder Reactions. -A new class of hydrazide-type organocatalyst is successfully applied in asymmetric Diels-Alder cycloadditions of α,β-unsaturated aldehydes (II) and (V) towards cyclopentadiene. Enantioselectivities of up to 96% e.e. are achieved. The reaction mechanism is discussed in detail. -(SUZUKI*, I.; ANDO, M.; SHIMABARA, R.; HIRATA, A.; TAKEDA, K.; Org. Biomol. Chem. 9 (2011) 8, 3033-3040, http://dx.doi.org/10.1039/c0ob01138j ; Hiroshima Univ., Minami, Hiroshima 734, Japan; Eng.) -Mischke 34-025