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 Dibakar C. Deka, Madeleine Helliwell and Eric J. Thomas p Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK Received 6 August 2001; revised 6 September 2001; accepted 27 September 2001 Abstract ÐDiels Alder reactions between cyclopentadiene and methyl E)-3-triphenylstannylpropenoate 8 and E)-3-triphenylstannyl- propenal 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 con®rmed by X-ray crystallography. Reduction and oxidation of this ester gave the exo-aldehyde 22 the structure of which was again con®rmed by crystal- lography. 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 con®rmed 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. q 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction Organotin halides and hydrides are widely used as reagents in organic synthesis. 1 Recently the introduction of enantio- merically enriched organotin halides and hydrides has been of some interest in the context of developing procedures for asymmetric synthesis. Reagents which are chiral solely at the tin tend to undergo ready racemisation, and so most of the chiral tin halides and hydrides which have been evalu- ated to date for asymmetric synthesis have made use of chiral ligands on the tin. 2±10 Since isopinocampheylboranes have found widespread use in organic synthesis, we decided to develop the chemistry of bicyclo[2.2.1]heptan-2-yl tin hydrides. 11 Of particular interest were such tin hydrides in which the tin was co-ordinated to a suitably positioned, heteroatom containing, functional group since this should help to determine the trajectory of donation of the hydrogen from the tin hydride. 5±7 With this goal in mind we prepared the exo-3-hydroxy- methyl- and 3-methoxymethyl-3-methyl-2-triphenylstannyl- bicyclo[2.2.1]heptanes 1 and 2. 12±14 Treatment with 1 equiv. of iodine led to cleavage of one of the phenyl groups from the tin to give the tin iodides 3 and 4 with NMR data suggesting that the tin in these tin iodides was partly co-ordinated to the oxygen of the hydroxyl or methoxy groups. 14 However, attempts to convert the tin iodide 3 into a tin hydride were unsuccessful and although the methoxy substituted tin hydride 5 could be prepared and there was some spectroscopic evidence in support of a small degree of co-ordination of the tin by the methoxy substituent, only racemic products were obtained when this tin hydride was used to reduce acetophenone and methyl 2-bromo-2-phenylpropanoate. Since amines are known to co-ordinate to tin halides and hydrides more effec- tively than ethers, 5±7 it was of interest to extend this work to Tetrahedron 57 2001) 10017±10026 Pergamon TETRAHEDRON 0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0040-402001)01035-3 Keywords: chiral organotin reagents; Diels Alder reactions; adducts. p Corresponding author. Tel.: 144-161-275-4614; fax: 144-161-275- 4939; e-mail: e.j.thomas@man.ac.uk