An unprecedented vanadyl(V) methoxide complex 4 derived from 3,5-dibromo-N-salicylidene-l-tert-leucinate enables highly enantioselective aerobic oxidations of alpha-hydroxyphosphonates at ambient temperature with selectivity factors ranging from 3 to >99.

A series of carbamates, amides, N-tosyl amides, (hetero)arenes, and hydrogen phosphines/phosphites has been examined as nucleophiles for (hetero)Michael-type additions to enones and enamides catalyzed by amphoteric vanadyl triflate under mild and neutral conditions. The newly developed C-N, C-P, and C-C bond-formation protocols were carried out smoothly in good to high yields without intervention of any 1,2-additions.

Chiral oxidovanadium(V) methoxides prepared from 3,5-disubstituted-N-salicylidene-l-tert-butylglycines and vanadyl sulfate in air-saturated MeOH serve as highly enantioselective catalysts for asymmetric aerobic oxidations and kinetic resolution of alkyl, aryl, and heteroaryl α-hydroxy-ketones with differed α-substituents at ambient temperature in toluene or TBME (tert-butyl methyl ether). The best scenarios involve the use of complexes which bear the tridendate templates derived from 3,5-diphenyl- or 3-o-biphenyl-5-nitro-salicyaldehyde. The kinetic resolution selectivities of the aerobic oxidation process are in the range of 12 to >1000 based on the selectivity factors (k(rel)).

A series of chiral vanadyl carboxylates derived from N-salicylidene-L-␣-amino acids and vanadyl sulfate has been developed. These configurationally well defined complexes were examined for the kinetic resolution of double-and mono-activated 2°alcohols. The best chiral templates involve the combination of L-tert-leucine and 3,5-di-t-butyl-, 3,5-diphenyl-, or 3,4-dibromo-salicylaldehyde. The resulting vanadyl(V)-methoxide complexes after recrystallization from air-saturated methanol serve as highly enantioselective catalysts for asymmetric aerobic oxidation of ␣-hydroxyl-esters and amides with a diverse array of ␣-, O-, and N-substituents at ambient temperature in toluene. The asymmetric inductions of the oxidation process are in the range of 10 to >100 in terms of selectivity factors (k rel) in most instances. The previously undescribed aerobic oxidation protocol is also applicable to the kinetic resolution of C-13 taxol side chain with high selectivity factor (k rel ‫؍‬ 35). X-ray crystallographic analysis of an adduct between a given vanadyl complex and N-benzyl-mandelamide allows for probing the stereochemical origin of the nearly exclusive asymmetric control in the oxidation process.alcohol oxidation ͉ ␣-hydroxy acids ͉ asymmetric catalysis ͉ vanadyl(V) methoxides T he oxidation of alcohols normally requires stoichiometric use of DMSO-based reagents or metal oxides of high oxidation state (1). Advances on their aerobic oxidations with catalytic metal oxides [e.g., RuO 2 -H 2 O (2), V 2 O 5 -K 2 CO 3 (3), and OsO 4 -Cu(O 2 CR) 2 (4)], homogeneous metal complexes [e.g., Co(OAc) 2 -N-hydroxyphthalimide (5), Ru(III)NOCl(salen) (6), RuCl 2 (PPh 3 ) 3 -hydroquinone-K 2 CO 3 (7), CuCl-Phen-DBADH 2 (8), RuCl 2 (PPh 3 ) 2 -TEMPO (9)͞CuCl-TEMPO (10), Pd(OAc) 2 -pyridine (11, 12), and Pd 4 Phen 2 (CO)(OAc) 4 (13)], bimetallic complexes [e.g., RuCl 3 -Co(OAc) 2 -aldehyde (14) and MoO 2 (acac) 2 -CuNO 3 ] (14, 15), or heterogeneous metal complexes [e.g., Ru(III) hydroxyapatite (16), polyaniline-supported MoO 2 (acac) 2 (17), and Pd(OAc) 2 -hydrotalcite-pyridine (18)] have been documented. Notably, additives and͞or bases are often needed to increase the catalyst reactivity and͞or to facilitate the turnover process. In addition, the targeted substrates are somewhat limited to primary, benzylic, allylic, and propargylic alcohols. Recently, the asymmetric variants of the aerobic catalytic process have attracted a lot of attention (19,20). So far, Pd(II)-sparteine (21, 22), photoly activated RuNOCl(salen) (23), and Mn(III)(salen)PF 6 (24) have been developed with fair to high enantioselectivity toward kinetic resolutions of 2°benzylic alcohols. In marked contrast, the asymmetric aerobic catalytic process with ␣-hydroxycarboxylic acid derivatives is relatively unexplored (25-31).Optically pure ␣-hydroxycarboxylic acid and mandelic acid derivatives are important precursors toward enantioselective synthesis scopes. Based on our experiences of using vanadyl and oxometallic species in catalyzing C-C and C-X bond forming (47-51), ae...