Tetra-n-Butylammonium Tribromide

Biographical Sketches

Valdemar B. C. Figueira studied Applied Chemistry - Organic Chemistry (1998-2003) at FCT/UNL in Lisbon, Portugal. He joined the research group of Prof. John Paul Jones at the University of North Wales, Bangor, UK in 2002 as an Erasmus student, working with quartz crystal microbalances.In 2003 he joined Prabhakar and Lobo’s research group under the project ‘Development of Synthetic Methodologies for Natural ­Algicides’ where he is currently with a doctoral fellowship from Fundação para a Ciência e Tecnologia (FC&T, Lisbon, Portugal).

Introduction

Tetra-n-butylammonium tribromide (TBATB) is one of the most widely used organic ammonium tribromides (OATB’s) for bromination [1-3] of several organic substrates.

Because it is a stable crystalline solid, easy to handle and maintains the desired reaction stoichiometry it is looked at as a substitute of Br₂. It can also be considered as a ‘greener’ brominating agent [4] as well as an in situ generator of anhydrous HBr.

Other types of reactions like acylation, oxidation and ­protection/deprotection of several functional groups can be performed with TBATB in catalytic amounts and under solvent-free conditions.

Preparation

Properties

Yellow-orange crystalline ionic solid, mp 75 °C (aceto­nitrile). IR bands at 170 and 190 cm^-1. Monoclinic space group C2/c structure determined by X-ray.

Abstracts

(A) Preparation of a wide variety of flavones and aurones starting from 2′-acetoxychalcones 1 in high yields (36-55% and 65-85%, respectively) was accomplished in two steps, being the first selective bromination with TBATB (70-80% for 2 and 75-85% for 3). [5]
(B) Direct condensation of various alcohols and carboxylic acids was efficiently achieved with a catalytic amount of TBATB under solvent-free conditions at reflux. Chemoselectivity for primary ­alcohols was observed when secondary and phenolic alcohols were also present. [6]
(C) Selective protection of various carbonyl compounds to the ­corresponding 1,3-oxathiolanes was performed with catalytic amount of TBATB. Chemoselective deprotection of synthesized 1,3-oxathiolanes to the parent carbonyl compounds was also obtained with TBATB. No bromination on α-keto position, aromatic ring, allylic position or double bond was observed. [7]
(D) Gosain and Sharma described the kinetics and mechanism for oxidation of vicinal and non-vicinal diols to the corresponding ­aldehydes and hydroxycarbonyl compounds, respectively. Ex­cellent yields were obtained. [8]
(E) Solvent-free, chemoselective diacylation of aldehydes was ­accomplished using a catalytic amount of TBATB, without side ­reaction yielding brominated products. Chemoselective cleavage of di­acylates was also reported with TBATB when the reaction was ­performed in different conditions. [9]
(F) TBATB promotes tetrahydropyranylation and detetrahydro­pyranylation of primary, secondary and tertiary alcohols when present in 10 mol%. Mild reaction conditions make both reactions compatible with other acid-sensitive groups such as OTs, nitro and Boc, among others. [10]

References

• 1 Mondal E. Bose G. Khan AT. Synlett  2001,  785 
• 2 Bose G. Li Y. Bhujarbarua PM. Kalita D. Khan AT. Chem. Lett.  2001,  30:  290 
• 3 Bose U. Chaudhuri MK. Dey D. Dhar SS. Pure Appl. Chem.  2001,  73:  93 
• 4 Bora U. Chaudhuri MK. Dehury SK. Curr. Sci.  2002,  82:  1427 
• 5 Bose G. Mondal E. Khan AT. Bordoloi MJ. Tetrahedron Lett.  2001,  42:  8907 
• 6 Naik S. Kavala V. Gopinath R. Patel BK. ARKIVOC  2006,  (i):  119 
• 7 Mondal E. Sahu PR. Bose G. Khan AT. Tetrahedron Lett.  2002,  43:  2843 
• 8 Gosain J. Sharma PK. Indian Acad. Sci. (Chem. Sci.)  2003,  115:  135 
• 9 Kavala V. Patel BK. Eur. J. Org. Chem.  2005,  441 
• 10 Naik S. Gopinath R. Patel BK. Tetrahedron Lett.  2001,  42:  7679