Synthesis and Crystal Structure Determination of [H2‐cryptand 222](Br₃)₂: A Unique Tribromide Catalyst for the Catalytic Chemoselective N‐Boc Protection of Amines

Abstract

The organic tribromide, [H 2 -cryptand 222](Br 3 ) 2 was synthesized and characterized by X-ray crystallography, and was utilized as an active catalyst for the N-boc protection of amines. The method is general for the preparation of N-boc derivatives of aliphatic (acyclic and cyclic), aromatic, primary and secondary amines. We also applied our new reaction protocols for the N-boc protection of some new amines and spectral and physical data for the obtained products are reported.

{[[K.18-Crown-6]Br3}n: A tribromide catalyst for the catalytic protection of amines and alcohols

“…In this continuation of our studies on the host-guest chemistry of crown ethers [18,[21][22][23][24] on the synthesis and application of tribromide reagents [18,19,21,22] and the protection of organic functional groups [21,22,25,26], we report that {[K.18-crown-6]Br3}n is an excellent catalyst for the tert-butoxycarbonylation of various amines and TMS and THP of alcohols under mild conditions. Thus, we prepared a range of tert-butoxycarbonylated amines under the following reaction conditions: amines (1 mmol), Diboc (1 mmol), {[K.18-crown-6] Br3}n (0.001 mmol), and ethanol (5 ml) as the optimized solvent for this reaction (Scheme 1 and Table 2).…”

“…Chemicals were purchased from Merck. The protected products were characterized by the comparison of their spectral (IR, 1 H-NMR, and 13 C-NMR) and physical data with those of known samples [21][22][23][24][25][26][27][28]. {[K.18-crown-6]Br3}n was prepared according our previously reported procedure [18].…”

“…For this purpose, many protective groups have been developed [20]. For a functional group, there are various protecting protocols: N-tert-butoxycarbonylation of amines by di-tert-butyl dicarbonate (Diboc) [21] and silylation and tetrahydropyranylation (THP) of alcohols by hexamethyldisilazane (HMDS) and 3,4-dihydro-2H-pyran (DHP) [22]. In this paper, we show the catalytic use of {[K.18-crown-6]Br3}n in the efficient N-boc protection of amines and protection in the reaction of alcohols to trimethylsilylation (TMS)-ether and THP-ether.…”

Synthesis and Cation Recognition Study of Novel Benzo Crown Ether Functionalized Enamine Derivatives

“…While the nitration of the benzo 18-crown-6 ether occurred in HNO 3 (70%) and CH 3 COOH at RT for 24 hr to obtained yellow colored 4-nitro benzo 18-crown-6 (5) in 77% yield which on further reduction by using NH 4 Cl and fresh Fe in ethanol at reflux condition to obtained 4-amino benzo 18-crown-6 ether (6) as a brownish solid in 67% yield. After that, we have synthesized substituted 3-(dimethylamino)-1-phenylprop-2-en-1-one compounds with excellent yield by using substituted acetophenone and dimethyl formamide dimethyl acetal in toluene under reflux condition [31,32] .…”

“…Since their discovery by Pederson in 1967, Crown ether are popular host compounds in host-guest chemistry along with their remarkable properties to complex metal cations have useful as synthetic ionophores, chromatographic stationary phase, ability to solubilize inorganic compound in organic solvent to increase their reactivity, phase transfer catalysts in organic synthesis, therapeutic reagents in chelate therapy as well as effective complexing reagents for the cations of alkaline earth and transition metal ions [3][4][5][6][7] . In addition, crown ether has extensive application in the field of science and technology and analytical chemistry such as pH sensors, construction of chemical switches, molecular recognition, metal ion probes, laser dyes, ion-selective electrode and organic conductors [8][9][10][11] .…”