Tributylstannane preparation

The alkynyl ketones 840 can be prepared by the reaction of acyi chlorides with terminal alkynes, Cul in the presence of Et3N is the cocatalyst[719]. (1-Alkynyl)tributylstannanes are also used for the alkynyl ketone synthesis[720]. The a,. 3-alkynic dithio and thiono esters 842 can be prepared by the reaction of the corresponding acid chloride 841 with terminal alkynes[721,722]. 

The o -diketone 865 can be prepared by the coupling of the acylstannane 864 with acyl chlorides[738,739]. The a-keto ester 868 is prepared by the coupling of (a-methoxyvinyl)tributylstannane (866) with acyl chloride, followed by ozo-nization of the coupled product 867[740,741],... 

In order to test whether this high level of diastereoselectivity is due to the stereoselective formation of 35 A, or a consequence of rapid equilibration between 35 A and 35 B, both reagents were selectively prepared via the tributylstannanes 38. Treatment of either reagent with chloro-trimethylsilane led to a similar ratio of the diastereomers 36 A/36B, with the anti-diastereomer 36A predominant in both reactions. 

A related convenient and mild method for the preparation of aliphatic and aromatic aldehydes in high yield from carboxylic acids is the reductive cleavage of l-acyl-3-methylimidazole-2-thiones by tributylstannane. 

Representative procedure for the synthesis of (Z)-a-selenenylvinylstannanes [34] A mixture of Cp2Zr(H)Cl (1.1 mmol) and (3-methoxy-l-propynyl)tributylstannane (1.0 mmol) in THF (5 mL) was stirred at room temperature for 20 min. A solution of PhSeBr (1.0 mmol) in THF (4 mL) (prepared in situ) was then injected into the resulting solution and the mixture was stirred at room temperature for 30 min. It was then diluted with light petroleum and stirred for a further 5 min., after which the supernatant was filtered through a short plug of silica gel. After evaporation of the solvent from the filtrate, the residue was purified by preparative TLC on silica gel to yield (lZ)-tributyl-[3-methoxy-l-(phenylse-leno) -1 -propenyl] stannane (60 %). 

The indolyltributylstannanes, which are more robust than their trimethylstannyl counterparts, are prepared similarly [166, 167]. Labadie and Teng synthesized the IV-Me, N-Boc, and jV-SEM (indol-2-yl)tributylstannanes [167], and Beak prepared the A-Boc trimethyl- and tributyltin derivatives in high yield [166]. Caddick and Joshi found that tributylstannyl radical reacts with 2-tosylindoles to give the corresponding indole tin compounds as illustrated [168]. 

The stereospecific preparation of Z- ,/l-dill uorostyrenes was accomplished by Davis and Burton via modification of the Heinze methodology, as illustrated in equation 4937,38. The Z- /,/i -di II uorostyrenes could be readily converted to other synthons, such as E- /i-di -/ -iodostyrenes ( -FIC=CFPh) and -a, / -difluoro-/ -tributylstannanes (E-PhFC=CFSnBu3), by known literature reactions38, and which could be utilized as synthons in other coupling reactions. 

Members of the she same compound class, arylethenylpurines, can also be prepared in a two step sequence. The cross-coupling of a halopurine with vinyl-tributylstannane leads to the formation of a vinylpurine, which in turn can undergo palladium catalyzed Heck reaction with a series of aryl halides (8.20.),28 The two step procedure is of particular interest, since the alternate approach, the Heck reaction of halopurines and arylethenes is of very limited scope. 

In contrast, the use of the tributylstannane 201 allows the preparation of a variety of 3-substituted pyrrolidines 202, by treatment of the same organolithium intermediate 199 with different electrophiles (Scheme 54)93. 

Additions of the transient y-OMOM crotyl indium chloride reagents to a-oxyge-nated aldehydes are strongly reagent-controlled. Thus the (R) and (S) reagents add to protected threose and erythrose aldehydes with high diastereoselectivity (Eq. 59) [75]. These additions are complementary to those previously effected with the y-BusSn counterparts (Eq. 45). It is thus possible to prepare precursors to the eight diastereomeric hexoses and their enantiomers from threose- and erythrose-derived aldehydes and their enantiomers plus the a-OMOM crotyl tributylstannane enantiomers. 

The tributyltin enolates 74 are readily prepared from the corresponding enol acetates and tributyltin methoxide in the absence of solvent [34]. The tin enolates thus obtained occur in the 0-Sn form and/or the C-Sn form, and both species can be used for the aldol reaction of this system. Although the tin enolates themselves have adequate reactivity toward aldehydes [34c], in the presence of the BINAP silver(I) catalyst the reaction proceeds much faster even at -20 °C. Optimum conditions entail the use of THF as solvent and the results employing these conditions in the catalytic enan-tioselective aldol reaction of a variety of tributyltin enolates with typical aromatic, a,/3-unsaturated, and aliphatic aldehydes are summarized in Table 2. TTie characteristic features are (i) All reactions proceed to furnish the corresponding aldol adducts 75 in moderate to high yield in the presence of 10 mol % (i )-BINAP AgOTf complex at -20 °C for 8 h, and no dehydrated aldol adduct is observed (ii) with an a,j3-unsaturated aldehyde, the 1,2-addition reaction takes place exclusively (entry 3) (iii) a bulky alkyl substituent of tin enolate increases the enantioselectivity of the aldol reaction. For instance, the highest ee (95 % ee) is obtained when the tin enolate prepared from pinacolone 77 or rert-butyl ethyl ketone 79 is added to aldehydes (entries 2, 7, and 8) (iv) addition of the cyclohexanone-derived enol tributylstannane 78 (( )-... 

Tributylstannane is prepared according to a published method, via an exchange between bis(tributyl)oxide and a polysiloxane containing Si—H bonds. ... 

Johnston and coworkers reported a base-free aryl amination method based on radical additions to azomethines through nonconventional addition pathways (equation 6)42,43. By this route, the aryl radical adds to nitrogen, rather than to the carbon of the ketimines. For example, the ketimine prepared from o-bromophenethylamine and acetophenone was subjected to tributylstannane and the radical initiator AIBN to give the corresponding indoline in 87% yield. The only side product observed was the directly reduced compound. The fact that only the intramolecular radical addition can afford the high yield limited its application in synthesis of other arylamines. 

Tributylstannyl ethers are normally prepared by reaction of alcohols with hexabntyldistannoxane, more commonly known as bis(tribntyltin) oxide, in benzene or toluene at reflnx, with removal of water. Holzapfel et al. noted that the reaction in benzene reqnires only 0.5 molar eqnivalents of bis(tribntyltin) oxide to go to completion, bnt takes 16 h at reflux. They can also be prepared nnder mild conditions by reaction of the alcohol with tributylstannane in the presence of catalytic triflic acid, or better with allyltribntyltin (Scheme 5.1.5). Polymer snpported versions of tribntyltin ethers have been prepared. ... 

C(6) position of the pyrone nucleus [126]. Interestingly, allenylstannane. readily prepared from propargyl tosylate by copper-mediated addition of lithium tributylstannane, was coupled with 2-iodothiophene to provide a rapid entry to 2-thienylallene (187) [127],... 

Alternatively, trialkylstannylcesium compounds can be prepared by fluoride ion-induced desilylation. Treatment of (trimethysilyl)tributylstannane with cesium fluoride affords a tributylstanyl anion. The anion reacts with a C-I bond to form a vinyl anion that promotes intramolecular cyclization [6]. The spiro ketone obtained is converted into a natural sesquiterpene acorone (Scheme 2.3). 

Primary tosylates are reduced by LiAlH4. The diacetal of D-fucose 5.39, an enantiomer of L-fucose, is thus prepared by reduction of tosylate 5.38 derived from the diacetal of D-galactose 5.11. A hydroxyl group can also be replaced by a halogen (Cl, Br, I) at any position of a protected sugar. The halide is easily reduced by a radical mechanism with tributylstannane, Bu3SnH (reaction 5.19). 

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