Tin-boron exchange reaction

Monobenzo fused borepins have been prepared by tin-boron exchange reactions (equation 18). Different stabilities to air were noted (208 R = OH) was air-sensitive <7lCC29l), but (208 R = Ph) had an unusual stability (67TL1263). 

Tin boron exchange reactions provide a convenient route to diborylated acetylene (equation 33). Diborylalkynes show an enhanced Lewis acidity in comparison to dibory-laUcanes as demonstrated by the coordination of THF in (31), but a lack of binding to the related alkyldiborane (32). This effect has been attributed to the stronger inductive electron-withdrawing effect of sp-hybridized relative to sp -hybridized carbons. ... 

X = S, O, NR). Lithium-, sihcon, or tin boron exchange provide facile access to the desired borylated species. On the other hand siloles and stannoles (X = Si, Sn) with organoboron substituents in the 3-position are conveniently prepared via organoboration reactions. Another new... 

Although ring-annulated and highly substituted borepins have been known for some time, simple 1-substituted borepins have only been thoroughly studied over the past decade. The discovery of a facile synthetic ronte to 1-snbstituted borepins through tin-boron exchange has much opened up the chemistry of these 7-membered boracycles. The chloro-substituted borepin (145) serves as a highly useful precursor to many other borepin derivatives via substitution reactions with nucleophiles (Scheme 20). In addition, several transition metal complexes of 1-borepins have been reported. 

These compounds are the most stable of the three classes of organothal-lium(III) derivatives and have been prepared by a wide variety of classical organometallic procedures. Many exchange reactions of TIX3 (X = Cl, carboxylate) with organo derivatives of boron, mercury, tin, lead, etc., have been shown to result in formation of R2TIX compounds 73, 78), but are of relatively little preparative significance. The most frequently used procedure... 

Enantiomerically pure glycosyl stannanes gave, after tin-lithium exchange and reaction with oxiranes in the presence of boron trifluoride diethyl ether complex, alkylation products as diastereomers (1 1 -2 1 d.r.) with complete retention at the stereogenic center a to the oxygen atom41. 

These complexes, which are readily synthesized by transmetalation see Transmetalation) from the appropriate Cp metal and MX4 (L = U) or (jj -L)MX3 (L L ), represent a large family of qnite always air-stable componnds. The bromides and iodides are also obtained from chlorine exchange reactions with the appropriate boron trihalide. The flnorides can be obtained by metathesis see Metathesis) of chlorides derivatives with MesSnF. With only one equivalent of tin reagent per mole of dichloride, partial fluorination occms affording mixed hahde metallocenes. The fluorides are also prepared by chloride/fluoride, by chloride/NMe2 followed by NMe2/fluoride exchange, and by oxidative addition see Oxidative Addition). ... 

For less activated aromatic systems (those without a nitro substituent), the halogen-exchange reaction has been investigated with potassium fluoride in a variety of polar aprotic solvents in the presence or absence of a catalyst (see Table 13). Many different types of catalysts have been investigated these include crown ethers.169 quaternary ammonium salts,163 164 phos-phonium salts,158167 aminophosphonium salts.162 compounds containing a phosphorus and an amino function,161 and inorganic fluorides of boron, aluminum, tin, phosphorus, titanium and zirconium.162 Different forms of potassium fluoride have been used these include spray-dried potassium fluoride,167 freeze-dried potassium fluoride,168 potassium fluoride recrystallized from methanol,165 and potassium fluoride dispersed oil calcium fluoride.166... 

Tin-lithium exchanges. A method for the preparation of a-hydroxy boronic esters takes advantage of the facile Sn/Li exchange of a-stannylalkyl MOM ethers. Subsequent reaction of the lithioalkyl ethers with boronic esters displaces one of the alkoxy groups of the latter." The reaction of chiral A-tributylstannylmethyl-2-methoxymethylpyrrolidine with BuLi and then aldehydes gives diastereomeric mixtures of P-amino alcohols. ... 

Exchange reactions between stable organometallics and palladium salts are useful for preparing isomerically pure organopalladium species to be used in situ for insertion reactions. Exchanges have been made with organocobalt , -iron , -phosphorus , -silicon , -lead , -tin , -boron , -thallium , -zinc , -magnesium and -mercury . Of these, mercurials are most often used, e.g. ... 

Another protocol uses a similar tin-iodine(III) and silicon-iodine(III) exchange reaction of (diace-toxyiodo)arenes or iodosylbenzene with tetraphenylstannane or (trimethylsilyl)benzene in the presence of boron trifluoride etherate [397]. 

The organotin derivative (7) was prepared from D-mannose, and some reactions involving Sn-Li exchange were studied, while the relative reactivities of some C-triphenylstaimyl-carbohydrate derivatives in iodine-induced phenyl-tin bond cleavage reactions have been determined. Nucleophilic addition of a carbanionic carborane to a number of sugar aldehydes has provided adducts that were used in attempts to increase the water solubility of carborane - antibody complexes with a view to localising boron on tumors prior to... 

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