Facile Syntheses of Oxazolines and Thiazolines with N-Acylbenzotriazoles under Microwave Irradiation

Abstract

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.

A new methodology for the synthesis of N-acylbenzotriazoles

“…[1][2][3][4][5][6][7][8][9] N-acylbenzotriazoles are one of the most useful benzotriazolederivatives which have been successfully utilized to prepare numerous biologically relevant compounds under neutral and mild conditions by N-, C-, S-, and O-acylations. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] In recent years our group has been involved in exploration of the synthetic utility of N-acylbenzotriazoles to make sugar amides by N-acylation, 25 benzoxazoles and N-phenylamides by benzotriazole ring cleavage 26,27 and ureas, carbamates and thiocarbamates by the Curtius rearrangement. 28 The earlier synthetic methods for conversion of carboxylic acids to N-acyl benzotriazole i.e.…”

Solvent‐Free Tandem Synthesis of 2‐Thiazolines and 2‐Oxazolines Catalyzed by a Copper Catalyst

“…General methods for the synthesis of 2-thiazolines and 2-oxazolines can be divided into two categories: one is the simple cyclodehydration of hydroxy thioamides [10] or hydroxy amides; [11] another one is the condensation of carboxylic acids, [12] esters, [13] nitriles, [14] N-acylbenzotriazoles, [15] or aldehydes [16] with amino thiols or amino alcohols. Recently, transition metal catalysts such as molybdenum oxide, [11c] RuCl 2 (PPh 3 ) 2 , [16a] and tungstophosphoric acid [14] were also involved in the preparation of these synthetically valuable compounds.…”

Five‐Membered Heterocycles: 1,3‐Azoles

“…The SOCl 2 was needed to complete the cyclization of the intermediate amide formed. This procedure is also convenient for the synthesis of thiazoline derivatives [349]. Several other derivatives of carboxylic acids can be used for the synthesis of oxazoline.…”