1.3- Disubstituted distannoxanes

Combination of a nonracemic isocyanate and a l,3-disul)sliluted distannoxane has provided a new method for determination of the optical purity of chiral alcohols (Scheme 12.174) [316]. When a chiral alcohol was reacted with commercially available (l )-l-(l-naphthyl)efhyl isocyanate in the presence of 1,3-disubstituted distannoxane, formation of the desired carbamates occurred rapidly, with acid-labile functional groups such as ester, THP and /Miydroxyketone remaining intact. Subsequent HPLC analysis of the resulting carbamate revealed a pair of well-separated peaks of diastereomers derived from both enantiomeric alcohols. 

In the semisynthesis of pachtaxel from fhe 10-deacetylbaccatin III derivative, 1,3-disubstituted distannoxane-mediated deacetylation played a pivotal role, giving rise to the formation of the desired secondary alcohol even in the presence of several functional groups (Scheme 12.188) [344]. Bis(tributyltin)oxide [329] and 1,3-disubstituted distaimoxane are excellent deacylation catalysts, and the synthetic utihty of bis(tributyltin)oxide has been revealed in regio- [345] and chemoselective deacylation (Schemes 12.189 and 12.190) [346]. 

Shanzer and Mayer-Shochet have utilized disubstituted stannoxanes as covalent templates for the formation of tetralactones. In this procedure, a dialkyl stannoxane is condensed with a glycol to form a cyclic-distannoxane as illustrated below. In a typical preparation, the distannoxane (i) was dissolved in CCI4 (ca. 0.04 At) at reflux and sebacoyl chloride (2 eq) was added dropwise at reflux. After heating for 20 h, the solution was concentrated to a solid. Chromatography afforded the tetralactone in 30% yield. ... 

As an extension of the auto-association in organotin compounds, the 119Sn chemical shifts of a series of functionally disubstituted symmetrical distannoxanes, X.R2SnOSnR2.X, containing a range of X substituents have been measured (5, 6, 37, 73) and some results are shown in Table IX. 

Both esterification and transesterification are classical reactions that still find great demands in modern synthetic chemistry.258,259 1,3-Disubstituted tetrakis(fluoroalkyl) distannoxanes, (XR2SnOSnR2Y)2 (R = C6Fi3C2H4 and... 

Previous reports on the reactivity of DBTO with alcohols and organic carbonates point out its transformation into 1,3-disubstituted tetra -butyl-distannoxanes under reaction conditions (Scheme 21.13a). ° " ° ... 

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