Narayan G. Bhat

A novel synthesis of β-ketosilanes via organoboranes

Abstract A convenient, novel synthesis of β-ketosilanes based on ( Z )-1-bromo-1-alkenylboronate esters is developed. α-Bromo-( Z )-1-alkenylboronate esters readily available using literature procedures smoothly undergo a reaction with trimethylsilylmethyllithium in tetrahydrofuran to provide the corresponding ‘ate’ complexes. These ‘ate’ complexes will undergo intramolecular nucleophilic substitution reactions to afford the corresponding ( E )-trisubstituted olefins containing trimethylsilylmethyl moiety. The oxidation of these intermediates with sodium acetate and hydrogen peroxide provides β-ketosilanes in good yields (63–75% yield).

A simple synthesis of B -2 - (1 -trimethylgermyl -1 -alkyl )- 1,3,2-dioxaborinanes. Isolation and selective oxidation to 1 -trimethylgermyl -1 -alkanols

Abstract ( Z )-1-Trimethylsilyl-1-alkenes easily prepared by the hydroboration of the corresponding 1-trimethylsilyl-1-alkynes followed by protonolysis with acetic acid, readily react with dibromoborane-methyl sulfide complex in dichloromethane for 6 h. The resulting solution is then treated with 1,3-propane diol in a 1:1 mixture of dichloromethane and n -pentane at 0°C for half an hour to provide the corresponding gem -dimetalloalkanes containing boron and silicon. These alpha-trimethylsilylalkylboronate esters are purified by vacuum distillation in high yields (72–84%) and the structures of these novel intermediates are further confirmed by selective oxidation with alkaline hydrogen peroxide to provide the corresponding alcohols containing trimethylsilyl group.

Simple procedures for the preparation of (Z)-2-(1-trimethylsilyl-1-alkenyl)-1,3,2-dioxaborinanes

Abstract Two simple procedures for obtaining (Z)-2-(1-trimethylsilyl-1-alkenyl)-1,3,2-dioxaborinanes based on 1-trimethylsilyl-1-alkynes are described. In the first procedure, 1-trimethylsilyl-1-alkynes are hydroborated with diisopinocampheylborane to provide the corresponding (Z)-2-(trimethylsilyl-1-alkenyl)-diisopinocampheylboranes. These are then reacted with excess acetaldehyde to afford the corresponding (Z)-2-(1-trimethylsilyl-1-alkenyl)-diethoxyboranes which are esterified with 1,3-propane diol to give the (Z)-2-(1-trimethylsilyl-1-alkenyl)-1,3,2-dioxaborinanes in good yields and in high stereochemical purities. In the second procedure, 1-trimethylsilyl-1-alkynes are hydroborated with dichloroborane–methyl sulfide complex in the presence of a stoichiometric amount of boron trichloride in hexane, followed by treatment with 1,3-propane diol. These novel stereodefined gem-alkenyldimetallic compounds containing boron and silicon are isolated and characterized by NMR (1H and 13C) spectral data.

A highly diastereoselective synthesis of (E)-B-2-(1-cyclopropyl-1-alkenyl)-1,3,2-dioxaborinanes. Isolation and oxidation to alkyl cyclopropyl ketones

A convenient, novel synthesis of alkyl cyclopropyl ketones based on Z-1-bromo-1-alkenylboronate esters is developed. α-Bromo-(Z)-1-alkenylboronate esters readily available from literature procedures smoothly undergo a reaction with cyclopropylmagnesium bromide in tetrahydrofuran to provide the corresponding ‘ate’ complexes. These ‘ate’ complexes undergo intramolecular nucleophilic substitution reactions to provide the corresponding (E)-1-alkenylboronate esters containing cylcopropyl moiety for the first time in good isolated yields (68–82%). The carbon skeleton present in these intermediates is confirmed by oxidation with hydrogen peroxide and sodium acetate to afford the corresponding alkyl cyclopropyl ketones in good yields (72–85%).

Functions Containing at Least One Metalloid (Si, Ge, or B) Together with Another Metalloid or Metal

This chapter deals with the preparation of compounds containing an sp3 carbon linked to a metalloid (Si, Ge, or B) together with another metalloid or metal. In the first part, the synthesis of compounds bearing two metalloids such as two silicons, two germaniums, two borons, a silicon and a germanium, a silicon and a boron, and a germanium and a boron are reviewed. The second part reports the access to compounds with a metalloid and a group 1 or 2 metal, a group 13 or 14 metal, and a transition metal. Also reported in the second part are synthetic routes leading to α-lithiogermyl alkanes, α-metallogermyl alkanes, α-lithioboryl alkanes, and α-metalloboryl alkanes.