Y-stannylation

In contrast to the reaction of y-stannyl alcohol 50, the y-stannyl benzyl ether 53 results in selective cleavage of the butyl-tin bond by reaction with (PhIO)n 18/DCC/BF3 and, after quenching of the reaction mixture with aqueous NH4C1, afforded the chlorostannane in high yield. Interestingly, the chlorostannane both in solution and in the solid state adopts a 1,3-diaxial conformation through Sn-O hypervalent interaction [82]. 

IOB alone can oxidize some alcohols, but catalysed oxidations are much more efficient. Thus, in the presence of RuCl2(PPh3)2 primary aliphatic alcohols were oxidized cleanly to aldehydes, at room temperature the use of m-iodosylbenzoic acid instead of IOB considerably increased the yields for example, hexanal was formed from hexanol quantitatively (by GC) [19], Another catalytic system involved the use of simple lanthanide salts such as ytterbium triacetate [20]. Cyclic y-stannyl alcohols, readily available from cyclic vinyl ketones and Bu3SnLi, underwent oxidation accompanied by carbon-carbon bond cleavage (Grab fragmentation), when treated with IOB.BF3 and DCC. The products were unsaturated aldehydes or ketones. 

Fragmentation of the isomeric mixtures of y-stannyl alcohols was achieved by adding a preformed solution (stir for 1 h at room temperature) of BF3 Et20 and DCC to the stannane and iodosylbenzene at 0 C, under a N atmosphere. Fragmentation of five-, six- and seven-membered ring stannanes proceeded... 

Table 1 Iodine(in)-me

Generation of Enantioenriched, Configurationally Stable Organolithium Reagents. (1 S,2E)-1 -(N.Af-Diisopropyl-carbamoyloxy)-l-methyl-2-butenyllithium-(—)-sparteine is configurationally stable in solution and is obtained by kinetic resolution of the racemic 2-alkenyl carbamate by n-butyllithium-(—)-sparteine with >80% de (eq 4). The enantioenriched allylstan-nane, obtained on y-stannylation, was used as chiral homoenolate reagent. The methoxycarbonylation (a, inversion) yields enantioenriched 3-alkenoates. ... 

Cyclopropanes 11 and 13, respectively, are obtained when y-stannyl alcohols 10 or 12 are treated with thionyl chloride or with acids (cf. Section 1.1.). 

The a-germylation is a reflection of kinetic control, whereas y-stannylation is thermodynamic controlled. The C-Ge bond is stronger than the C-Sn bond. D(Ge-Et) = 237 kJ mok, D(Sn-Et) = 193 kJ mok. a-Germyl ester (2) played the role of a Ge-masked dienolate equivalent. Thus, Lewis acid-mediated addition of the a-germyl ester (2) to an acetal (Scheme 11.6) [17, 18], diefhylazodicarboxylate... 

When e-oxoallylstarmanes, prepared from carbostannation of 2,3-dimethylbuta-diene, were reacted with aldehydes in the presence of Bu2SnCl2, a-adducts were obtained exclusively and no y-adducts were observed. This complete regioselectivity is ascribable to intramolecular coordination of carbonyl group to y-stannyl group (Scheme 12.25) [63]. 

The chiral bis(sulfonamide) catalyzed cyclopropanation was extended successfully to y-silyl-and y-stannyl-substituted allylic alcohols, for example, giving cyclopropanes 90 and 91.109... 

A y-stannyl or y-silyl substituent is not affected in the Pd(0)-catalyzed allylic 1,3-rearrangement... 

Fragmentation. y-Iodo and y-stannyl ketones derived from cycloalkenones are converted into unsaturated ketones. The reagent combinations are amphiphilic. 

Table 1 Iodine(IlI>-niediated 1,4-nagmentation of y-Stannyl Alctritols ...

Recently, Lewis acidic hydrostannane was shown to be valuable for highly stereoselective homolytic hydrostannylation of allyl and homoallyl alcohols. Using EtsB-dry air as radical initiator, the hydrostannylation of Morita-Baylis-Hillman (MBH) adduct 1 took place smoothly, and subsequent buty-lation of the reaction mixture with BuLi gave y-stannylated alcohol 2 in 64% yield with good syn diastereoselectivity (Scheme 4.1). Following treatment with pyridine and thionyl chloride, syn-2 could be easily transformed into trans-, l-disubstituted cyclopropane 3 in 85% yield." ... 

Ketones related to (149) provide ready access to Y-stannyl tertiary alcohols (150), which are known to undergo oxidative... 

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