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Concerning the 1,5-stereocontrol in tin(IV) chloride promoted reactions of 4- and 5-alkoxyalk-2-enylstannanes: trapping intermediate allyltin trichlorides using phenyllithium.

Organic & biomolecular chemistry (2012-08-14)
Lindsay A Hobson, Eric J Thomas
ABSTRACT

Transmetallation of the 5-benzyloxy-4-methylpent-2-en-1-yl(tributyl)- and -(triphenyl)stannanes 1 and 8 using tin(iv) chloride generates an allyltin trichloride that reacts with aldehydes to give (Z)-1,5-anti-6-benzyloxy-5-methylhex-3-en-1-ols 2. The allyltin trichloride believed to be the key intermediate in these reactions has been trapped by phenyllithium to give anti-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 9. Transmetallation of this anti-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 9 generated an allyltin trichloride that reacted with aldehydes to give the (Z)-1,5-syn-6-benzyloxy-5-methylhex-3-en-1-ols 23 and was trapped by phenyllithium to give syn-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 24. Similar stereoselectivity was observed for tin(iv) chloride promoted reactions of this syn-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 24 with aldehydes and with phenyllithium. The allyltin trichlorides generated by transmetallation of 4-hydroxy- and 4-benzyloxy-pent-2-enyl(triphenyl)stannanes 34 and 35 were similarly trapped by phenyllithium to give 4-hydroxy- and 4-benzyloxy-pent-1-en-3-ylstannanes 36 and 37 whose configurations were established by correlation with known compounds. This work confirmed the configurations of the intermediate allyltin trichlorides involved in tin(iv) chloride promoted reactions of 4- and 5-alkoxypent-2-enylstannanes with aldehydes and showed that the high levels of remote stereocontrol were due mainly to kinetically controlled transmetallation. A fuller mechanistic scheme is proposed for the reactions in the 5-benzyloxy-4-methylpent-2-enylstannane series together with relevant (119)Sn NMR data.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Tin(II) chloride, reagent grade, 98%
Sigma-Aldrich
Tin(II) chloride dihydrate, ACS reagent, 98%
Sigma-Aldrich
Tin(II) chloride dihydrate, reagent grade, 98%
Sigma-Aldrich
Tin(II) chloride, anhydrous, powder, ≥99.99% trace metals basis
Sigma-Aldrich
Tin(II) chloride dihydrate, ≥99.995% trace metals basis
Sigma-Aldrich
Tin(II) chloride dihydrate, puriss. p.a., ACS reagent, reag. ISO, reag. Ph. Eur., ≥98%
Sigma-Aldrich
Tin(II) chloride, ≥99.99% trace metals basis
Supelco
Tin(II) chloride dihydrate, suitable for AAS
Sigma-Aldrich
Tin(II) chloride dihydrate, ≥99.99% trace metals basis