Molybdenum Oxides as Highly Effective Dehydrative Cyclization Catalysts for the Synthesis of Oxazolines and Thiazolines

Abstract

In the presence of molybdenum oxide the dehydrative cyclization of N-acylserines, N-acylthreonines, and N-acylcysteines can be carried out under Dean-Stark conditions in toluene to give oxazolines and thiazolines. The ammonium salts (NH(4))(6)Mo(7)O(24).4H(2)O and (NH(4))(2)MoO(4) have excellent catalytic activities for the dehydrative cyclization of serine and threonine derivatives, and the acetylacetonate complex MoO(2)(acac)(2) has a remarkable catalytic activity for the dehydrative cyclization of cysteine derivatives. In addition, polyaniline-supported MoO(2)(acac)(2) can easily be recovered and reused.

Synthesis of the Biologically Active Natural Product Cyclodepsipeptides Apratoxin A and Its Analogues

“…Another approach is from the cysteine amide by dehydrative cyclization using a thiol group. [9][10][11][12] As the thiol-protected amino acid residue is labile for acid, base, oxidation, and reduction, it would be preferable to avoid using the thiol-protected residue in any total synthesis that involves long reaction steps. Wipf and Uto elegantly demonstrated that the oxazoline moiety was ringopened to the corresponding thioamide on a cyclic peptide by treatment with H 2 S, and then dehydrative cyclization using N,N-dimethylaminosulfur trifluoride (DAST) led to the total synthesis of the thiazoline-containing cyclic peptide trunkamide A.…”

Total Synthesis of Thuggacin B

“…Removal of the trityl protecting group liberated the thiol group which was cyclized to give the thiazoline using Mo complex 17, which was disclosed by Sakakura et al very recently. [14] Other Lewis acids including the related [MoO 2 -(acac) 2 ] [15] did not effect ring closure in sufficient yields.…”

An Exploration of the Metal Oxide-assisted Decomposition and Rearrangement of N-Acyl-1,3-oxazolidin-2-ones Leading to 2-Aryl-2-oxazolines [1]

“…These include the high-temperature dehydrative coupling of benzoic acids and amino-alcohols [30 -34], Lewis acid-catalysed addition and subsequent ring closure of a combination of aryl-nitriles and amino-alcohols [35,36], or ring expansion via the rearrangement of N-acylaziridines [37]. Oxazoline rings can also be produced via N-(2-hydroxyethyl)amides promoted by reagents such as DAST [38 -40], DeoxoFluor [40], SnCl 2 Bu 2 [41], the Vilsmeier reagent [42], Martin's Sulfurane [43], substituted triazines [44], the Burgess reagent [45,46], PPh 3 /CCl 4 [47], molybdenum oxides [48], arylboronic acids [49], zeolites [50], and TsOH [51], among others [52].…”