Abu T. Khan

Effects of Substituents in the β-Position of 1,3-Dicarbonyl Compounds in Bromodimethylsulfonium Bromide-Catalyzed Multicomponent Reactions: A Facile Access to Functionalized Piperidines

1,3-Dicarbonyl compounds can be converted to Mannich-type products A or highly functionalized piperidines B in the presence of a catalytic amount of bromodimethylsulfonium bromide (BDMS). The combination of aromatic aldehyde, amine, and 1,3-dicarbonyl compounds in the presence of a catalytic amount of BDMS leads to the formation of Mannich-type product A when R is a non-enolizable carbon or an alkoxy group, whereas in cases when R = CH3, the same combination yielded highly functionalized piperidines B. A synthetic study and mechanistic proposal are presented.

An environmentally benign synthesis of organic ammonium tribromides (OATB) and bromination of selected organic substrates by tetrabutylammonium tribromide (TBATB)

Abstract Stable crystalline organic ammonium tribromides (OATB), like Me4NBr3, Et4NBr3, Bu4NBr3, cetyltrimethylammonium tribromide, PyHBr3, can be readily synthesised from the reaction of the corresponding bromides with V2O5 and aqueous H2O2. Typically, TBATB, Bu4NBr3, brominates a variety of organic substrates rather easily under mild conditions. An activated aromatic ring is selectively brominated in the presence of an olefinic double bond.

A useful and convenient synthetic protocol for interconversion of carbonyl compounds to the corresponding 1,3-oxathiolanes and vice versa employing organic ammonium tribromide (OATB)☆

A wide variety of carbonyl compounds 1 can be easily protected selectively as the corresponding 1,3-oxathiolanes 2 in good yields using a catalytic amount (0.01–0.1 equiv.) of n-tetrabutylammonium tribromide in dry CH2Cl2 at 0–5 °C. On the other hand, various 1,3-oxathiolanes 2 can be deprotected chemoselectively to the parent carbonyl compounds 1 employing 0.5 equivalents of organic ammonium tribromides under identical conditions in very high yields. Mild conditions, high selectivity and yield, highly efficient, less expensive, and no brominations either at the double bond or allylic position and even α- to the keto position or aromatic ring are some of the major advantages of the protocol.

An environmentally benign synthesis of aurones and flavones from 2′-acetoxychalcones using n-tetrabutylammonium tribromide

Abstract A wide variety of aurones ( 3a–f ) can be prepared exclusively from 2′-acetoxychalcones ( 1a–f ) in high yields in two steps, by bromination using n-tetrabutylammonium tribromide (TBATB) in the presence of CaCO3 in CH2Cl2–MeOH (5:2) at 0–5°C followed by cyclization of the brominated products 2a–f on treating with 0.2 M ethanolic KOH solution at 0–5°C, respectively. In contrast various flavone derivatives 6a–f can be obtained exclusively from compounds 1a–f in fairly good yields, by brominating with the same reagent in CH2Cl2, followed by dehydrobromination and finally cyclization on treating with 0.1 M NaOMe solution.

A Simple and Convenient One-Pot Synthesis of Benzimidazole Derivatives Using Cobalt(II) Chloride Hexahydrate as Catalyst

Abstract A simple and efficient method for the convenient synthesis of 2-arylbenzimidazole has been described on reaction with o-phenylenediamine and various aromatic aldehydes using cobalt(II) chloride hexahydrate as a catalyst. The method is cost-effective, high-yielding, clean, and selective.

Nickel(II) chloride as an efficient and useful catalyst for chemoselective thioacetalization of aldehydes

Abstract A wide variety of acyclic and cyclic dithioacetals can be prepared chemoselectively from the corresponding aldehydes by employing a catalytic amount of nickel(II) chloride in dry CH 2 Cl 2 –MeOH (5:1) at room temperature in good yields. Some of the major advantages of this procedure are high chemoselectivity, ease of operation, high yields and also compatibility with other protecting groups.

Regioselective Synthesis of 2H - Pyrano [3, 2-c] Benzopyran-5H-One and 3H-Pyrano [2, 3-c] Benzopyran-5H-ONE

Abstract The hitherto unreported title compounds were obtained in good yields by [3, 3] sigmatropic rearrangement of 4 - [2-propynyloxy] coumarin and 3 - [2-propyny-loxy] coumarin respectively.

Total synthesis of R-(+)-patulolide A and R-(−)-patulolide B: The macrolides isolated from Penicillium urticae mutant

Abstract The title compounds (2E, 11R)-4-oxo-2-dodecen-11-olide, 1 and (2Z, 11R)-4-oxo-2-dodecen-11-olide, 2 were synthesised in optically pure forms from a nitroalkane synthon involving a chiral resolution step using goat liver lipase.

Regioselective Synthesis Of 4-Aryloxymethyl-2h-Pyrano 3,2-C Benzopyran-5H-One From 1-Aryloxy-4-Coumarinyloxy But-2-Yne#

Abstract 1-Aryloxy-4-(4′-coumarinyloxy) but-2-yne (1) on refluxing in chlorobenzene gave 4-aryloxymethyl-2H-pyrano 3,2-c benzopyran-5H-one as the single product in almost quantitative yield. All the eight butynes studied underwent 3,3,7 sigmatropic rearrangement at the 4-(4′-coumarinyloxy) propynyl part to give pyranocoumarin derivatives and no furanocoumarin derivative was formed at all.

A simple and convenient synthetic protocol for O-isopropylidenation of sugars using bromodimethylsulfonium bromide (BDMS) as a catalyst.

Various O-isopropylidene derivatives of sugars and acyclic sugars were obtained in very good yields on reaction with acetone at room temperature with a catalytic amount of bromodimethylsulfonium bromide (BDMS). These O-isopropylidene derivatives can also be prepared in good yields on reaction with 2,2-dimethoxypropane (DMP) in acetonitrile using the same catalyst in shorter reaction times. Some of the advantages of this method are high effectiveness, a nonaqueous workup procedure, economic viability, and good yields.