Cycloaddition phosphoramidite ligands

Najera et al. have shown that Feringa s phosphoramidite ligand 102 is superior to other ligands in the cycloaddition of aryl iminoesters 62 with tert-butyl acrylate (106), /V-methylphthalimide 114, and diisopropyl fumarate (118).57 As shown in Scheme 2.31 and Table 2.9, the products 116 and 117 were formed in excellent yields and exquisite endo selectivity. 

The AlCl3-catalysed 3-I-2-cycloaddition of diethyl frans -2,3-disubstituted cyclopropane-1,1-dicarboxylates and aromatic aldehydes produced diethyl 2,5-diaryl-4-benzoyltetrahydrofuran-3,3-dicarboxylates in moderate to good yields and with excellent diastereo-selectivities. The palladium-catalysed 3 -f- 2-cycloaddition of trimethylenemethane with aldehydes produced methylenetetrahydrofurans in good yields and with good enantioselectivities. A novel phosphoramidite ligand possessing a stereogenic phosphorous (29) was used in this transformation. ... 

Trost and coworkers reported a novel palladium-catalyzed [3 + 2] cycloaddition of trimethylenemethane with ketones. This protocol provides access to highly enan-tioenriched tetrahydrofurans bearing a tetrasubstituted stereocenter (Scheme 2.4). In this process, the use of a Cl-symmetric phosphoramidite ligand is critical for establishing this reaction, which demonstrated a uniquely high activity under the reaction conditions [10]. 

Use of the phosphoramidite ligand (-)-199 proved to be crucial for the enantioselective rhodium-catalyzed crossed [2 + 2 + 2] cycloaddition of alkenyl isocyanate 197 with phenylacetylene 198, which provided the vinylogous amide 200 in 62% yield (98% ee). Thereafter, cycloaddition product 200 underwent a diastereoselective hydrogenation followed by a Mitsunobu reaction to complete the total synthesis of (+)-lasubine II (201). 

Hayashi and coworkers have developed the highly efficient enantioselective intramolecular [5+2] cycloaddition of heteroatom (O and NTs) alkyne-VCPs 31 under rhodium catalysis [29]. High enantioselectivities of up to >99% ee were achieved for the corresponding cycloadducts 32 by the use of the chiral phosphoramidite ligand 33 in combination with a catalyst such as [RhCKCaH lJi- The reactions were performed at 30 °C in dichloromethane as the solvent and in the presence of sodium tetrakis(3,5-bis(tiilluoromethyl)phe-nyl)borate (Barp) as source of anionic counterion, which produced a series of chiral heteroatom (O and NTs)-tethered cycloadducts in high yields, as shown in Scheme 20.13. 

Asymmetric 1,3-dipolar cycloadditions of azomethine imines with terminal alkynes have been catalysed by 11 chiral ligand (8) coordinated metal amides to form N,N-bicyclic pyrazolidinone derivatives. Mechanistic studies have established the factors that determine the regioselectivity of the stepwise reaction. Novel phosphoramidite ligands (9) coordinated with palladium have been used to effect enantioselective synthesis of pyrrolidines by 3-P 2-cycloaddition of trimethylenemethane (from 2-trimethylsilylmethyl allyl acetate) to a wide range of imine acceptors (Scheme 11). ... 

The CuBr2/amine-promoted 2 + 2-cycloaddition reaction of 1,4-bisallenes (17) produced bicyclo[4.2.0]octadiene derivatives (18) in a one-pot procedure (Scheme 7) Phosphoramidite ligands (19) activate the Au(I)-catalysed 2 + 2-cycloaddition reaction of A-allenylsulfonamides with styrenes, at -70 C, to form vinyl cyclobutane derivatives in high yields and enantioselectivity. A new Pt(II) catalyst with a hollow-shaped tri- ethynylphosphine activates the intermolecular 2 + 2-cycloaddition reaction of allenyl silyl ether with vinyl ethers to yield methylenecyclobutanes in good yield. 

The Lewis acid-catalysed 3 + 2-cycloaddition of cyclopropanes with aldehydes yields tetrahydrofurans with high diastereoselectivity.22 The enantiospecific Sn(II)-and Sn(IV)-catalysed formal 3 + 2-cycloadditions of aldehydes with donor-acceptor (g) cyclopropanes produce optically active tetrahydrofurans23 The bulky phosphites and phosphoramidites are excellent ligands which promote the Pd-catalysed 3 + 2-intramolecular cycloaddition between alkylidenecyclopropanes and alkynes24 The... 

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