A simple synthesis of 2-substituted oxazolines and oxazines

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

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.

Facile syntheses of oxazolines and thiazolines with N-acylbenzotriazoles under microwave irradiation

Microwave reactions of 2-amino-2-methyl-1-propanol (2) or 2-aminoethanethiol hydrochloride (4) with readily available N-acylbenzotriazoles 1a-j in the presence of SOCl(2) produced 2-substituted 2-oxazolines 3a-j in 84-98% yields and 2-substituted thiazolines 5a-i in 85-97% yields, respectively. With use of this method chiral oxazoline 6, bisoxazoline 7, bisthiazoline 8, and 5,6-dihydro-4H-1,3-oxazines 9 or 10 have also been prepared in 82-96% yields. These results demonstrate a new application of N-acylbenzotriazoles in the preparation of oxazolines and thiazolines under mild conditions and short reaction times with microwave irradiation.

Parallel synthesis of oxazolines and thiazolines by tandem condensation-cyclodehydration of carboxylic acids with amino alcohols and aminothiols

A combinatorial library of oxazolines and thiazolines was synthesized in moderate to excellent yields using a newly developed methodology. Free carboxylic acids were directly condensed with amino alcohols and aminothiols in the presence of 3-nitrophenylboronic acid as a dehydration catalyst. The library synthesis illustrates the scope of this process: After traditional reaction optimization, a total of 17 oxazolines and 6 thiazolines were successfully prepared in a 24-reaction setup in a Radleys GreenHouse parallel synthesizer. The yields of the parallel reactions ranged from moderate to excellent, depending largely on carboxylate reactivity and functionalization, and generally exceeded those of the traditional reaction setup. The target compounds were isolated in high purities (average purity is 96% according to GC analysis) after passing reaction mixtures through short PrepSep SPE Florisil cartridges.