[100045-83-8] · C15H34O2Sn · Tri-n-butyl[(methoxymethoxy)methyl]stannane · (MW 365.20)
(hydroxymethyl anion equivalent1)
Physical Data: bp 117 °C/0.34 mmHg.
Solubility: sol THF.
Analysis of Reagent Purity: by gas chromatographic analysis on a 0.25 mm × 30 m DB-1701 fused silica capillary column, 12 psi column pressure, 120-250 °C at 10 °C/min, then 250 °C; retention time: 13.1 min. 1H NMR (300 MHz CD-Cl3): d 0.8-1.1 (m, 15H), 1.2-1.7 (m, 13H), 4.02 (d, 2 H, J = 4.5 Hz).
Preparative Methods: the most convenient preparation involves the two-step procedure outlined in eq 1.2 The first step involves the addition of Tri-n-butylstannyllithium to Paraformaldehyde as described by Still.2,8 In the second step, methoxymethylation is achieved via acetal exchange with Dimethoxymethane, promoted by Boron Trifluoride Etherate and Molecular Sieves.2,6 This procedure provides the desired reagent in higher yields compared to an alternative procedure which uses Phosphorus(V) Oxide to promote the acetal exchange step.9 This method is also superior to an alternative approach which involves alkylation of (tributylstannyl)methanol with Chloromethyl Methyl Ether.10
Purification: by filtration through alumina followed by distillation.2
Handling, Storage, and Precautions: as with all organostannanes, precautions should be taken to avoid all contact with tributyl[(methoxymethoxy)methyl]stannane. The reagent should be handled in a fume hood. The reagent can be stored neat in a freezer under nitrogen for several months.
Tributyl[(methoxymethoxy)methyl]stannane undergoes tin-lithium exchange with n-Butyllithium to generate the organolithium intermediate (1), a hydroxymethyl anion equivalent. (1) adds to ketones to form monoprotected 1,2-diols in very good yield (eq 2), and the acetal protective group can be removed under mild acidic conditions (eq 3).1 This stannane reagent complements the (isopropoxydimethylsilyl)methyl group as a hydroxymethyl anion equivalent, since the latter group is converted to alcohol using oxidative basic conditions.3
The stannane reagent has been added to a variety of carbonyl compounds. Aldehydes4 and lactones5 react with (1) in a manner analogous to the ketone example above. Other substrates include b-alkoxy enones (eq 4)6 and a,b-unsaturated carbonyl compounds.7 In the latter case, the intermediate tertiary alcohol formed by 1,2-addition of (1) is converted by oxidation to a 3-substituted a,b-unsaturated enone (eq 5).
In synthetic work, tributyl[(methoxymethoxy)methyl]stannane is preferred over the closely related (ethoxyethylmethyl)tributylstannane developed earlier by Still.8 Since the MOM ether reagent does not contain a chiral center, the formation of diastereomeric intermediates is avoided.
Karen R. Romines
The Upjohn Company, Kalamazoo, MI, USA