Synthesis of chiral organotin reagents: synthesis and X-ray crystal structures of bicyclo[2.2.1]heptan-2-yl(diphenyl)tin chlorides with cis-disposed nitrogen containing substituents

Abstract

Diels Alder reactions between cyclopentadiene and methyl ( E)-3-triphenylstannylpropenoate 8 and ( E)-3-triphenylstannylpropenal 14 gave predominantly the adducts 18 and 19 in which the triphenyltin substituents were in the exo-positions. Alkylation of the ester 18 took place from the endo-face with excellent stereoselectivity to give the exo-ester 20 the structure of which was confirmed by X-ray crystallography. Reduction and oxidation of this ester gave the exo-aldehyde 22 the structure of which was again confirmed by crystallography. Treatment of the aldehyde 22 with hydroxylamine and O-methylhydroxylamine gave the oxime 23 and O-methyl oxime 25, in which one of the phenyl groups had been lost from the tin together, in the latter case, with the expected triphenylstannyl substituted O-methyl oxime 24. The structures of oximes 23 and 25 were confirmed by X-ray crystallography which showed clear evidence for co-ordination of the tin by the nitrogen. The aldehyde 22 was also converted into the hydrazone 26, loss of a phenyl substituent from the tin not being observed in this case although the double-bond had been reduced in situ. The loss of the phenyl groups observed during the reactions between the aldehyde 22 and hydroxylamine and O-methylhydroxylamine may be due to steric congestion in these systems.