Stannanes: Stille coupling with

Pyridine 117 undergoes a Stille coupling with l-methyl-2-trimethylstannylpyrrole to give 118 in 36% yield [83], and the same stannane has been joined with bromopyrimidines [84]. 

These workers also synthesized tryptamine stannane 161 and effected Stille couplings with this compound, including the intramolecular reaction 162 to 163 [171]. Eight- and 9-membered rings could also be fashioned in this manner. Other Pd catalysts were much less successful. The N-tosyl derivative of 162 was similarly prepared and used in Stille chemistry. 

Recently, Li successfully conducted the Suzuki and Stille reactions on the pyrazine ring of 3-bromoquinoxalin-2-ylamines [51]. Indolylquinoxaline 92 was obtained from the union of 3-bromoquinoxalin-2-ylamine 90 and l-phenylsulfonyl-2-tri-n-butylstannyl-l//-indole (91). A wide variety of heterocyclic stannanes bearing various functional groups underwent Stille coupling with 90 under the same conditions to give the corresponding adducts in 72-98% yields. 

If 2,3-dibromo propene is used as an allylic substrate the substitution product 71 can be either isolated or, after addition of additives and adjustment of the reaction conditions, 71 can readily react in cross-coupling reactions with alkynes (Sonogashira coupling), stannanes (Stille coupling), or boronic acids and boronates (Suzuki coupling) to provide the sequential allylic substitution-cross-coupling products 72-78 in moderate to good yields (Scheme 23). 

Equally, a 1.5 1 mixture of cis- and frans- 1,3-dibromo propene reacts with sodium dimethyl methylmalonate to furnish the vinyl bromo derivative 79 in excellent yield, which in turn is transformed in a one-pot fashion to a 1.5 1 mixture of enyne 80 or the corresponding Suzuki products 81 and 82 (Scheme 24). Interestingly, (( )-3-bromo-propenyl)-tributylstannane furnishes the vinyl stannane 83 upon allylic substitution that instantaneously is subjected to the conditions of a Stille coupling with iodo benzene to give the sequence s product 84 in 68% yield (Scheme 25). 

Later, the dimethylphenylsilyl adduct 75 d was not only converted to the vinyl-ketene acetal 81 by a Wittig-Horner reaction via the ester 80, but also by reduction of 80 to the aldehyde 84 followed by silylation of the corresponding anion to the silylenol ether 85. Vinylcyclohexenes without terminal substitution (e. g., 83) was prepared via an alcohol derived from 80 or 84 [73,74]. The least substituted diene 83 was alternatively prepared from the triflate 82 in a Stille coupling with trialkylvinyl stannane [75] (Scheme 24), a reaction also used by Toshima etal.[76]. 

Hydrogenation with Raney nickel removes the chiral auxiliary and, as we had hoped, hydrogenates the alkene from the less hindered exo-face, pushing the side chain inside the folded molecule 83. The ketone is converted into the only possible vinyl triflate for Stille coupling with a vinyl stannane to give the diene 84. 

Stille coupling with aryl tris-(perfluorohexylethyl)stannane as a reaction component (aryls also comprise furyl and pyridyl) [65,66]. 

Stille couplings with 2,6-dichloropurine occur selectively at C-6, however the selectivity is reversed when chlorine is replaced by bromine or iodine at C-2. A similar pattern is seen for 6,8-dichloropurine, the 6-chlorine again being the more reactive. 8-Bromo-diaminopurines, after prior masking by silylation, undergo normal coupling with heteroaryl stannanes. ... 

Tin Derivatives A convenient and direct method for the preparation of metallated species in the azole series starts with lithiation, as in the case of rr-excessive systems. In thiazoles the initial lithiation is in the 2-position. Subseqnent qnenching with a stannyl halide will furnish a stannane snbstrate 100 to be used for Stille couplings with aryl or heteroaryl halides, in the present case with a bromide (Scheme 42). Stannylated oxazoles are similarly prepared and react in the same manner.The same applies to their benzannulated analogs 101. ... 

In a Pd-catalyzed sequence, allenyl stannanes undergo Stille coupling with P-iodoacrylic acids 36 followed by annulation to 4,5,6-substituted 2H-pyran-2-ones 37 [14] ... 

Scheme 5-61. Aryl Stille coupling with an allyl stannane. ...

Vinylation can also be done by Pd-catalysed cross-coupling in which one component is used as a halide or triflate and the other as a stannane (Stille reaction) or boronic acid (Suzuki reaction). Entry 9, Table 11.3, is an example of the use of a vinylstannane with a haloindole. lndole-3-boronic acids, which can be prepared by mcrcuration/boration, undergo coupling with vinyl triflates (Entry 10). 

The Suzuki coupling of arylboronic acids and aryl halides has proven to be a useful method for preparing C-aryl indoles. The indole can be used either as the halide component or as the boronic acid. 6-Bromo and 7-bromoindolc were coupled with arylboronic acids using Pd(PPh3)4[5]. No protection of the indole NH was necessary. 4-Thallated indoles couple with aryl and vinyl boronic acides in the presence of Pd(OAc)j[6]. Stille coupling between an aryl stannane and a haloindole is another option (Entry 5, Table 14.3). 

Scheme 5.2-19 Pd-catalyzed Stille coupling of a-iodoenones with vinyl and aryl stannanes in...

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