Synthesis of chiral organotin reagents: Diels–Alder reactions of methyl 3-(triphenylstannyl)acrylate: synthesis of diphenyl(3-substituted bicyclo[2.2.1]heptan-2-yl)tin hydrides
Cyclopentadiene undergoes Diels–Alder reactions with methyl (E)- and (Z)-3-(triphenylstannyl)acrylates 5 and 6 to give the endo-cycloadduct 9, and a mixture of the exo- and endo-isomers 10 and 11, respectively. The endo-product 9 is reduced to the alcohol 12 which is protected as its methyl ether 13. Attempts to remove one of the phenyl substituents from the tin using iodine are complicated by destannylation to the tricyclic iodide 14. However, after hydrogenation, treatment with 1 mol equivalent of iodine gives the tin iodide 17 which is reduced to the tin hydride 18. The hydroxyalkyltin hydride 21 is similarly prepared. The unsaturated tin hydrides 24 and 26 have been prepared by reduction of the Diels–Alder adducts 23 and 25 obtained from cyclopentadiene and methyl (Z)-3-(chlorodiphenylstannyl)acrylate. The tin hydrides 18 and 21 are found to undergo free-radical reactions as exemplified by addition to methyl propiolate and reductive dehalogenation of the iodo lactone 30.