- Process for the preparation of 1,3,2-oxazaborolidine compounds
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A process is used for the preparation of 1,3,2-oxazaborolidine compounds. This process prepares compounds of formula (I) or (IA): in which: R1 is an alkyl or an aryl; and R2, R3, R4 and R5 are especially a hydrogen atom or an alkyl, wherein the following are reacted in two steps: a) a boric precursor compound with an acetal compound to give a boronate compound; and b) the boronate compound with an amino alcohol compound. This process avoids by-products and exhibits a very good stereospecificity.
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Page/Page column 7
(2008/12/06)
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- Organoboranes. 56. Systematic study of the reactions of 1-alkenylboronic esters with representative organolithium and grignard reagents to provide an efficient, selective synthesis of organyl-1-alkenylborinic esters
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A selective reaction of the ate complexes formed with 1-alkenylboronic esters and organolithium or Grignard reagents, by treatment with either Br?nsted or Lewis acids at -78 °C to give the corresponding organylalkenylborinic esters, is explored in this study. This systematic, detailed study reveals that the nature of the alkoxy group on boron, the nature and the amount of the alkyllithium or Grignard reagent used, the solvent, the reaction temperature, and the nature and amount of the acid used all play significant roles in influencing both the yield and the selectivity achieved for the formation of the desired organylalkenylborinates. Optimized procedures for the syntheses of representative organylalkenylborinic esters in high yield are summarized.
- Brown, Herbert C.,Vasumathi, Nagarajan,Joshi, Navalkishore N.
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p. 1058 - 1067
(2008/10/08)
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- Organoboranes. 31. A simple preparation of boronic esters from organolithium reagents and selected trialkoxyboranes
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The reaction of methyllithium with trimethoxyborane at -78°C in ethyl ether yields a mixture of methylated boranes and their corresponding ate complexes. We have found that under the same conditions triisopropoxyborane reacts cleanly with methyllithium to form the lithium methyltriisopropoxyborate complex. Protonation of this complex with anhydrous hydrogen chloride quantitatively yields methyl diisopropoxyborane. This reaction of organolithium reagent with triisopropoxyborane appears to provide a general, valuable route to boronic esters. Other alkoxyboranes were examined for their selectivity for monomethylation by methyllithium. In addition to triisopropoxyborane, triisobutoxyborane and tri-sec-butoxyborane also give the methylboronic esters quantitatively. This development provides the first general preparation of boronic esters from organolithium reagents.
- Brown, Herbert C.,Cole, Thomas E.
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p. 1316 - 1319
(2008/10/08)
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