Functional Group Transformations of Diols, Cyclic Ethers, and Lactones Using Aqueous Hydrobromic Acid and Phase Transfer Catalyst under Microwave Irradiation

Abstract

Synthesis of bromoalkanols has been achieved from diols, ethers, and lactones using aq HBr (48%) and tetrabutylammonium iodide/bromide as phase transfer catalyst under microwave irradiation. This environmentally benign route provides enhanced yields of products and does away with the use of benzene as compared to existing conventional methods. DiscussionBromoalkanols and bromocarboxylic acids are important intermediates in the synthesis of insect pheromones and other naturally occurring products, as they provide two reactive sites for further reaction. After suitable protection of alcoholic/acidic groups, these compounds can be important precursors for the formation of C-C bonds 1-3 and conversion to Wittig 4 or to a Grignard reagent. 5 Various methods have been reported in the literature to achieve this goal; however, they require reaction of diols with aqueous hydrogen bromide using a continuous extraction apparatus employing nonpolar solvents such as cyclohexane 5 (72 h) or toluene 6 (16 h). Kang et al. 7 have prepared bromoalkanols by refluxing a mixture of diols with 48% aq HBr in benzene in 40-90% yield; dibromide (13%) and unreacted diol (2%) were also present. Now, microwave energy has been used in a wide variety of reactions, 8-12 owing to their high heating efficiencies with remarkable rate enhancement and dramatic reduction in

Synthesis of Demissidine and Solanidine

“…We then looked for conditions that could activate C22 and thus trigger the designed Schmidt reaction. It was well-known that lactones could be opened with HBr or HCl to afford the corresponding ω-halo acids or esters . Under these conditions, the intramolecular nucleophilic azido group nearby would outdo the ambient halogen ions in attacking the electrophilic site.…”

Microwave and Ultrasound Assisted First Synthesis of 12-Hydroxyhentriacontane

“…Microwave irradiation 12 of a mixture 1,10-decanediol (2), 48% aq. hydrobromic acid and tetrabutylammonium iodide as phase transfer catalyst furnished 10-bromodecan-1-ol (3) in 80% yield followed by tetrahydropyranylation 13 by using DHP and iodine under microwave irradiation to yield 10-bromo-1-tetrahydropyranyloxydecane (4) in 94% yield.…”

Synthesis of 9,9′-[1,2-Ethanediylbis(oxymethylene)]bis-2-amino-1,9-dihydro-6H-purin-6-one, an Impurity of Acyclovir

“…The method is based in an unusual acid catalysed PTC process described in the 70s by Landini et al , who used it to convert primary alcohols into alkyl chlorides using aqueous HCl [23], to cleave ethers and esters with aqueous HBr, with conversion of the resulting aliphatic alcohols into bromides [24], or to add hydrohalogenic acids to alkenes, using aqueous solutions of the corresponding acid [25]. The method has been more recently improved by Goverdhan et al , with the use of microwaves, to cleave cyclic ethers to halo alcohols, lactones to haloacids or diols to haloalcohols [26]. …”