The asymmetric conjugate addition of various carbon and heteroatom nucleophiles to nitroalkenes as a tool for the construction of highly functionalized synthetic building blocks is presented. Diastereoselective, substrate-controlled 1,4-additions are also included. Besides auxiliary controlled asymmetric Michael additions, external asymmetric versions employing enantiopure additives, addition-elimination processes with enantiopure leaving groups, and catalytic asym-

Dedicated to Professor Hans Jürgen Bestmann on the occasion his 75th birthdayConsidering the enormous significance of organophosphorus compounds in nature, it is surprising that naturally occurring phosphonates [1] that contain a CÀP bond, have only been known since 1959 [2] when (aminoethyl)phosphonic acid was isolated from sheep rumen. Since then numerous compounds of this class have been isolated, synthesized, and tested for their biological activity. In particular, phosphonates [3] bearing heteroatomic substituents in the a-or bposition to the phosphorus atom have shown strong activities as antibiotics, anticancer drugs, herbicides, and enzyme inhibitors. [4] Their activity may be attributed to the similarity to the natural a-and b-amino acids and to the relative hydrolytic stability of the C À P bond compared to that of the P À O bond. Optically active a-hydroxy and a-aminophosphonic acids can nowadays be prepared by a variety of methods. [5] In contrast, only a few methods have been developed for the asymmetric synthesis of b-aminophosphonic acids [6] and of their precursors. A convenient route to b-aminophosphonic acids is provided by the addition of phosphorus compounds bearing a labile phosphorus À hydrogen bond to nitroalkenes, first developed by Pudovik et al., [7] and the subsequent reduction of the nitro group. [8] However, the addition of dialkylphosphites to aromatic nitroalkenes leads to extensive polymerization of the nitro compounds. Examples of addition of di-and trialkylphosphites to unsaturated nitro compounds were also described by Yoshimura et al., [9] who were able to add diethylphosphite to aliphatic nitroalkenes at 100 8C in moderate yields. Yamamoto et al. [10] developed the first substrate-controlled diastereoselective addition of dialkylphosphites to unsaturated nitrosaccharides, albeit only with moderate stereoselectivities. An efficient general method for the asymmetric Michael addition of phosphorus nucleophiles to unsaturated nitro compounds has not yet been described. Chiral catalysts [11] and chiral phosphorus nucleophiles [12,13] have already been employed in the asymmetric hydrophosphonylation of aldehydes and imines by 1,2-addition.We report here on the synthesis of an enantiomerically pure phosphite and its application as a chiral phosphorus nucleophile in the asymmetric Michael addition to aromatic nitroalkenes.We obtained phosphite (R,R)-2 in a two-step synthesis starting from TADDOL [14] ((R,R)-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyl-1,3-dioxolane) (R,R)-1, which was converted into the corresponding chloride with PCl 3 and finally hydrolyzed in almost quantitative yield (Scheme 1). [15] The C 2symmetry of the ligand avoided the formation of a new stereogenic center at phosphorus and the otherwise necessary separation of diastereomers.

[reaction: see text] A high-loading ROMPgel-supported thiazolium iodide was prepared via ROMPolymerization of the corresponding norbornene-derived monomer. The resulting ionic ROMPgel proved to be an efficient organic catalyst for Stetter reactions. The 1,4-dicarbonyl products, important intermediates in the synthesis of cyclopentenones and heterocycles, were obtained in high yields and excellent purities after minimal purification. The ROMPgel could be reused in up to four consecutive reaction cycles without significant loss of catalytic activity.

ROMPgel-supported ethyl 1-diazo-2-oxopropylphosphonate has been prepared, and the supported reagent has been effectively employed in the conversion of a variety of aldehydes into terminal alkynes under mild reaction conditions. The influence of cross-link structure, comonomers, and polymer structure on reaction efficiency has been examined. [structure: see text]

[reaction: see text]. The first asymmetric P-C bond formation under heterogeneous conditions was achieved via a Fe2O3-mediated conjugate addition of a chiral phosphite to alkylidene malonates. The easy cleavage of the chiral auxiliary from the addition products leads to optically active beta-substituted beta-phosphono malonates in good yields and high enantiomeric excesses.