N. G. Bhat

A simple, general synthesis of 1-alkynyldiisopropoxyboranes

Abstract A representative selection of 1-alkynyldiisopropoxyboranes has been prepared in high yields from the reaction of 1-lithio-1-alkynes and triisopropoxyboranes at −78° C, followed by treatment with hydrogen chloride.

A new convenient approach to the preparation of Z-1-alkenylboronates by the cis-hydrogenation of 1-alkynyldiisopropoxyboranes

Abstract Hydrogenation of 1-alkynyldiisopropoxyboranes over Lindlar catalyst in 1,4-dioxane proceeds cleanly to furnish Z-1-alkenylboronates in very high diastereoselectivity, 90–100%.

A simple conversion of [E]- into the isomeric [Z]-2-(1-substituted-1-alkenyl)-1,3,2-dioxaborinanes, providing a convenient stereospecific synthesis of both [E]- and [Z]-1,2-disubstituted vinyl bromides

Abstract A highly stereo- and regioselective conversion of [ E ]- into [ Z ]-2-(1-substituted-l-alkenyl)-1,3,2-dioxaborinane has been achieved for the first time. Treatment of these boronic acid esters with bromine, followed by base, produces either [ Z ]- or [ E ]-disubstituted vinyl bromides in good yields (76–81%) and excellent stereochemical purities (> 99%). Replacement of boron moiety with bromine proceeds with complete inversion.

Highly general synthesis of [E]- and [Z]-3-alkylsubstituted allylboronates via one-carbon homologation of stereospecific 1-alken-1-ylboronates

Abstract Stereospecific 1-alken-1-ylboronates readily react with in situ generated chloromethyllithium, producing the corresponding allylboronate in good yields and in excellent stereochemical purities. These are very important synthetic intermediates and conversion of a representative derivative, [ E ]-2-(2-heptenyl)-1,3,2-dioxaborinane, 2 (R 1 = C 4 H 9 , R 2 = R 3 = H), into several compounds of synthetic interest is described.

A novel route to 1,3-dienyl-2-boronic esters providing simple syntheses of conjugated [E,E]-dienes and conjugated [E]-alkenones.

Abstract A highly stereo- and regioselective synthesis of [ E ]-2-(1′-[ E ]-alkenylsubstituted-1′-alkenyl)-l,3,2-dioxaborinanes has been achieved for the first time via the nucleophilic substitution of [ Z ]-(1-bromo-1- alkenyl)boronic esters with [ E ]-l-lithio-l-alkenes. These are novel boron intermediates, which are converted into conjugated [ E,E ]-dienes and conjugated [ E ]-alkenones in good yields and in excellent stereochemical purities.

Chiral synthesis via organoboranes. 31. A simple synthesis of enantiomerically pure (Z)- and (E)-Alkenes, (Z)-RCHCHR* and (E)-RCHCHR*

Abstract The monoisopinocampheylorganylboranes, IpcR*BH, readily available in purities ⩾99% ee by the asymmetric hydroboration of alkenes with monoisopinocampheylborane, IpcBH 2 , are easily transformed into enantiomerically pure ( ⩾99% ce ) (Z)- and ( E )-alkenes. The generality of the procedure was demonstrated by synthesizing four each (Z)- and ( E )-alkenes. This new procedure makes the enantiomerically pure compounds readily available and contributes another stage to the completion of our goal of providing a truly general asymmetric synthesis of pure enantiomers.

Organoboranes for synthesis. 13. Simple, efficient syntheses of long-chain alcohols and carboxylic acids.

Abstract General, convenient and simple syntheses of long straight chain alcohols and carboxylic acids were developed utilizing organoborane chemistry. One of the methods entails the thermal isomerization of long-chain alkyldicyclohexylboranes, followed by oxidation. An alternative procedure for the preparation of long-chain alcohols involves the KAPA isomerization of internal alkynes to the terminal derivative, followed by dihydroboration with 9-BBN and oxidation. Alternatively, the terminal alkyne can be oxidised directly to the carboxylic acid. In another strategy, the C 30 -alcohol triaxontanol was prepared by employing high pressure carbonylation of a borane intermediate.

GENERAL SYNTHESIS OF ALKYLALKENYLALKYNYLBORANES VIA HALOBORANES

Die Methyl-alkylalkenylborinate (IIIb), dargestellt durch Hydroborierung der Alkine R1CCR2 mit den aus (I) durch Hydrierung erhaltenen Alkylbromoboran-Komplexen (II) und anschliesende Methanolyse, reagieren mit entsprechenden Alkinyl-Li-Verbindungen zu entsprechenden Li-methoxylalkylalkenylalkinylboraten, die bei Behandlung mit BF3 · OEt2 die gewunschten Titelverbindungen (IV) ergeben.