Arun K. Mandal

Novel transformations with borontrifluoride etherate/iodide ion : facile conversion of 2-ketooxiranes and 2-bromo-2-enones to the α,β-unsaturated carbonyl compounds

Borontrifluoride etherate/iodide ion rapidly deoxygenates α-ketooxiranes, 3, to the corresponding α,β -unsaturatad carbonyl compounds, 4, in near quantitative yields. In contrast, the reaction of 3 with borontrifluoride etherate/bromide ion, 2, yielded the corresponding 2-bromo-2-enone derivatives, 5, in excellent yields. The reagent 1, also dehalogsnates a variety of 2-bromo-2-enones, 5, to tha corresponding 2-en-1-one derivatives, 4, in high yields. We have recently reported that a combination of borontrifluoride etharate/halide ions (X=I, 1; X=Br, 2) performas number of useful synthetic transformations, e.g., cleavage of alkyl ethers to the halides and alcohols2 , non-aqueous conversion of acatals and ketals to the carbonyl compounds3 , and conversion of activated alcohols to the halides4. Vankar et al have also reported independantly the deoxyganation of sulfoxides to sulfide5 and the selective cleavage of benzyl ethers6 with the reagent, 1. In continuation of our work, we report herein an efficient deoxygenation of α-ketooxiranes, 3 (eqn.1) and dehalogenation of 2-bromo-2-enone, 5 (eqn.2) to the corresponding α, β-unsaturated carbonyl compounds, 4, with the reagent, 1.

Facile displacement of tetramethylethylene from thexylborane-triethylamine by treatment with olefins. a convenient synthesis of monoalkylborane derivatives

Abstract The reaction of thexylborane-triethylamine with representative olefins proceeds readily at 25° with the displacement of tetramethylethylene (TME) and the formation of the corresponding monoalkylborane-triethylamine adduct. This reaction provides a convenient synthesis in high yield of such monoalkylboranes and their derivatives.

Anomalies in the asymmetric hydroboration of olefins with the 11 adduct of (+)-α-pinene and BH3 · THF

The hydroboration of cis-2-butene and cis-3-hexene with pure diisopinocampheylborane (IPC2BH) and monoisopinocampheylborane (IPCBH2), both prepared from (+)-α-pinene, were studied. In contrast to IPC2BH, which yielded R-(−)-2-butanol and R-(−)-3-hexanol in 98.4 and 94.5% optical purities, IPCBH2 yielded S-(+)-2-butanol and S-(+)-3-hexanol in 23.6 and 19.7% optical purifies respectively. PMR examination of the methanolyzed products were utilized to establish the species present in the freshly prepared and aged 11 adduct from (+)-α-pinene and BH3 · THF. The results confirm the interpretation previously advanced for the major differences realized in asymmetric hydroboration with the fresh and aged 11 adducts.