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

Diels Alder reactions between cyclopentadiene and methyl (E)-3-triphenylsta nnylpropenoate 8 and (E)-3-triphenylstannylpropenal 14 gave predominantly t he 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 e xcellent stereo selectivity to give the exo-ester 20 the structure of which was confirmed by X-ray crystallography. Reduction and oxidation of this es ter gave the exo-aldehyde 22 the structure of which was again confirmed by crystallography. Treatment of the aldehyde 22 with hydroxylamine and O-meth ylhydroxylamine gave the oxime 23 and O-methyl oxime 25, in which one of th e phenyl groups had been lost from the tin together, in the latter case, wi th the expected triphenylstannyl substituted O-methyl oxime 24. The structu res of oximes 23 and 25 were confirmed by X-ray crystallography which showe d 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 b een reduced in situ. The loss of the phenyl groups observed during the reac tions between the aldehyde 22 and hydroxylamine and O-methylhydroxylamine m ay be due to steric congestion in these systems. (C) 2001 Elsevier Science Ltd. All rights reserved.