Stannanes reactions with carbonyl compounds

Scheme 9.6. Reactions of Allylic Stannanes with Carbonyl Compounds...

Scheme 9.6 gives some other examples of Lewis acid-catalyzed reactions of allylic stannanes with carbonyl compounds. 

The reactions of ailylboranes, -silanes and -stannanes with carbonyl compounds and imines always take place with double-bond migration, and the structural stability of the reagent is a common problem that is encountered ( 2.7). The reactions of ailylboranes and -boronates occur without catalysis, while those of allylsilanes and -stannanes usually require the presence of a Lewis add [253], The mechanism of the reactions of allylboron derivatives is concerted, and the addition occurs via a six-membered cyclic transition state. A slightly distorted chair transition state model in which the oxygen of the carbonyl group is coordinated to the boron atom is usually invoked (Figure 6.42). Various steric and polar interactions dictate whether the Si or Re face of the prochiral aldehyde is attacked (models C j... 

The synthesis of simple terminal alkenes has been reported by the reaction of (triphenylstannyl)methyllithium with carbonyl compounds [390]. (Phenylthio)-triphenylstannylmethyllithium and benzaldehyde can be selectively transformed into ( )-yS-(phenylthio)styrene or, alternatively, its Z-isomer via yS-hydroxyalkyl-stannane 241 by means of a tin-Peterson reaction (Scheme 2.148) [391]. LDA is usually used as the base in the tin-Peterson reaction. Butyllithium is not a suitable base for abstraction of the a-proton because lithium-tin exchange may occur [259]. 

Reactions of allylic stannanes with carbonyl compounds... 

Addition of Bu3SnLi or McsSnI.i to 4-t-butylcyclohexanone affords mixtures of trans and cis adducts in ratios that depend on reaction conditions (Table ll)68. In THF, a 93 7 mixture is obtained with both reagents. This ratio is thought to represent the thermodynamic distribution—the axial stannane being favored. In ether, the cis isomer predominates, suggesting a kinetic preference for equatorial addition. Each of the two isomers can be lithiated with BuLi. Subsequent treatment with alkyl halides or carbonyl compounds affords the substituted alkoxy cyclohexanes with retention of stereochemistry. 

Diazo compounds are photoreduced to hydrazines in the presence of silanes and stannanes in a process that apparently involves initial H-atom transfer to an excited state of the diazo compound.105 LFP studies of reactions of Bu3SnH with excited states of diazo compounds 40 and 41 found fast reactions. The singlet diazo species reacted with Bu3SnH about as fast as singlet carbonyl compounds, whereas the triplet diazo species reacted with tin hydride somewhat slower than triplet excited states of carbonyl compounds.100,105... 

The Lewis acid-mediated addition of allyl silanes and allyl stannanes to carbonyl compounds has been a topic of interest for many years [103,104]. Stereochemical studies of reactions of allylsilanes and allylstannanes with aldehydes have included FeCl3-mediated intramolecular reactions (Sch. 20) [105],... 

Takuwa and his coworkers have demonstrated that the irradiation of the aromatic carbonyl compounds (120) in the presence of the stannanes (121) affords the unsaturated alcohols (122) as the principal products. An electron transfer mechanism is proposed. Electron transfer is also involved in the reaction of amines with alkenes such as the phenylethylenes (123). The electron transfer in this instance affords an alkenyl radical anion the presence of which has been demonstrated by a variety of techniques. A further reaction has been uncovered in the photoreaction of, for example, the alkene (123a) with iV, AT-diethylani lino in the presence of carbon dioxide. This treatment affords the three carboxylated derivatives (124), (125), and (126) by trapping of the radical anion by carbon dioxide. Similar carboxylation was demonstrated for (123b) and biphenyleno. The influence of the amine on the yield of product was studied. ... 

The reaction of fluoromethyl phenyl sulfone with diethyl chlorophosphate at room temperature requires the use of 2 eq of base ( -BuLi, LDA, LiHMDS) to give the lithium salt of diethyl 1-(phenylsulfonyl)-l-fluoromethylphosphonate, which can be hydrolyzed and isolated in 73% yield or reacted in situ with a large variety of carbonyl compounds to form the corresponding a-fluorovinyl phenyl sulfones in moderate to good yields (44-95%, Scheme 3.9). - These sulfones are readily converted into 1-fluoroalkenes via the corresponding (fluorovinyl)stannanes. ... 

Chiral titanium complexes 4 and 5, which were developed as chiral catalysts for asymmetric carbonyl-ene reactions with prochiral glyoxylate esters [50], were first apphed to the catalytic asymmetric allylation of carbonyl compounds by Mikami and Nakai (Scheme 5) [9]. The titanium catalysts are prepared from (S)-binaphthol and diisopropoxytitanium dihahde (X=C1 and Br) in the presence of 4 A molecular sieves. Using these catalysts, glyoxylates are enantio- and diastereoselectively allylated with allylic trimethylsilanes or allylic tributylstan-nanes. High levels of enantioselectivity and syn selectivity are observed for (E)-crotylsilane and -stannane. The syn selective allylation reaction is believed to proceed mainly through an antiperiplanar transition state. 

Full details have appeared of the a-oxo-lithiation of 2,6-disubstituted benzoate esters (6) having sterically protected carbonyl groups (c/. 3,133). Reaction of the lithio derivatives, formed from (6) by reaction with excess base or regenerated from the stannane (7) by treatment with stoicheiometric methyl-lithium, with alkyl halides or carbonyl compounds followed by ester cleavage leads to alcohols and diols, respectively (Scheme 9). 

Addition of tributylstannyl-lithium to crotonaldehyde and protection of the resulting alcohol with chloromethyl methyl ether gives the stannane (192), which reacts with both alkyl and aryl aldehydes RCHO to form specifically the t/rr o-hydroxy-enol ethers (193). These latter compounds have been used to prepare tra/i5-4,5-disubstituted butyrolactones by hydrolysis and subsequent oxidation. Palladium-catalysed carbonylation of RX in the presence of organotin species constitutes a useful synthesis of unsymmetrical ketones, and in the example reported this year RX is an arenediazonium salt. The reaction, which is basically an aromatic acylation, proceeds in good to excellent yield. Another Pd-catalysed reaction of aromatics, this time aryl bromides, is their reaction with acetonyltributyltin (194), prepared from methoxytributyltin and isopropenyl acetate, to give the arylacetones (195). ... 

In many instances, the scope of the reactions listed above is limited as to the functional groups that are unaffected. Except for aryl-stannanes and arylfluorosilanes, carbonyl functionalities are often not compatible with the reactions. A number of cross-coupling reactions are known of aryl triflates [64 a] and arylfluorosulfonates [64b] with aryl stan-nanes catalysed by Pd(0)-complexes (Stille reaction) [65], aryl zinc chlorides [64b], and aryl boron compounds (boronic acids and esters, Suzuki reaction [66]). Aryl stannates are relatively stable to air and moisture and many funetional groups are tolerated. The coupling reaction using Ar-X/Ar-SnR3 can be accelerated by Cu(I) [67] or Ag(I) [68] catalysis. 

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