Stannanes quinoline

In respect to the Suzuki and the Negishi couplings, quinoline stannanes provide an easy entry to highly substituted derivatives. As a highlighted example, 2-trimethylstannyl-5,8-dimethoxyquinoline reacts with appropriately substituted pyridyltriflate in the presence of palladium tetrakis-(triphenylphospine), lithium chloride, and copper bromide to produce 2-pyridylquinoline, an advance intermediate for the total syntheses of antitumor compounds streptonigrin and lavendamycin. ... 

The reductive cyclization protocol was then applied to a suitably A-protected radical precursor to allow further access to the alkaloid calothrixin B. Satisfactorily, 2-indolylacyl radicals derived from A-(methoxymethyl) selenoester 57 underwent cyclization under TTMSS-AIBN conditions with an even higher efficiency than their A-methyl counterparts. The reaction nevertheless followed a different course as, after the radical addition and quinoline rearomatization, pentacyclic phenol 58, a fully aromatic tautomeric form of ketone P, was isolated in 90% yield. The same phenol 58 was isolated although in lower yields (50-70%) using either stannane-AIBN or AIBN-irradiation protocols. 

Yamamoto and Yanagi [24] have prepared iodoazines through iodo-destannation of trimethylstannylazines. Trimethylstannyl sodium was prepared in situ from chlorotrimethyl-stannane and metallic sodium. Subsequent treatment of 2-chloroquinoline 25 with trimethylstannyl sodium gave 2-trimethylstannylquinoline 41. Likewise, 3- and 4-trimethyl-stannyl quinolines 42 and 44 were converted to 3- and 4-iodoquinolines 43 and 45 in 96 and 91% yield, respectively via iodo-destannation. In the same fashion, 2,4-bis (trimethylstannyl)quinoline was synthesized from 4-bromo-2-chloroquinoline using two equivalents of trimethylstannyl sodium in 65% yield. 

With this substrate (28) the ring closure can be conveniently accomplished with either stannyl or sulfanyl radicals with no concomitant formation of the six-membered-cyclization quinoline product, which is present instead, or is predominantly formed, in all of the reaction mixtures obtained with group other than TMS. At the same time, both radical precursors, that is, stannane and thiol, can serve as nucleophiles for the intermediate indolenines 29 and 31, which are trapped to give the final substituted indoles 30 and 32 with high efficiency. 

Stannylated azines have been widely used for cross-coupling. Al-Oxides of tri(n-butyl)stannylated pyridine, quinoline, and isoquinoline and tti(n-butyl)stannylated N-methiodides of pyridine and quinoline have been coupled with heteroaryl halides (Scheme 61). The use of tosylate as a counterion for the quatemized salts 149 and 150 minimized decomposition of the stannane whereas iodide anion promotes destannyla-tion.f ... 

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