Synthesis of chiral organotin reagents: synthesis of bicyclo[2.2.1]heptan-2-yl(diphenyl)tin hydrides with cis-disposed, oxygen-containing substituents
Alkylation of the methyl 3-triphenylstannylbicyclo[2.2.1]hept-5-ene-2-carboxylate 3 using lithium diethylamide and either methyl iodide or benzyl bromide at –78 °C is stereoselective in favour of the endo-alkylated products 10 and 11. Methylation of the saturated ester 12 is also endo-selective in favour of 13. If the unsaturated ester 3 is deprotonated at 0 °C rather than at –78 °C, the rearranged stannane 17 is obtained as a side-product. The endo-triphenylstannylbicyclo[2.2.1]heptane-2-carboxylate 22 has been prepared from the ester 12 by phenylselenylation, oxidative elimination and reduction using diimide. The triphenylstannanes 13, 17 and 20 have been converted into the alkyl(diphenyl)tin hydrides 27, 28 and 29 and the methoxyalkyltin hydride 36 has also been prepared and characterized. These tin hydrides accelerate the reduction of aryl methyl ketones to 1-arylethanols by phenylsilane, but the reduction product is racemic. Syntheses of the aminobicycloalkyl(triphenyl)stannanes 44, 45 and 48 are described.