Dienyne stannane

Ni(COD)2-catalyzed tandem carbostannylation of alkynes and allenes with alky-nylstannes in the presence of a phosphine ligand results in highly chemoselective synthesis of dienyne stannanes. The stereoselectivity of the reaction depends strongly on the chelation nature of the ligands [237]. For example, when tris(4-tri-fluoromethylphenyl)phosphine is used, the D/E ratio is 98 2. On the other hand, when a bidentate ligand (e.g. [o-(dimethylamino)phenyl)diphenylphosphine] is employed, the D/E ratio becomes 6 94. 

Another intriguing cascade, of an intramolecular Heck type followed by an intermolecular Stille coupling, produces the dienyne 80 starting from the enyne 78 and the stannane 79 (Scheme 3-24) [175]. The reversed sequence of a Stille-type followed by a... 

A neat combination of some of the foregoing chemistiy is use of the cyclic stannane (48) as an equivalent of the 1,4-pentadienyl dianion (49). Thus, treatment of the stannane (48) with Bu"Li, copper(I) iodide-dimethyl sulfide complex and the iodoallene (50) smoothly leads to the dienyne (51) and thence, by a repetition of this sequence but using electrophile (52), to 3-dehydroarachidonic acid methyl ester (53). 

It is known that the reaction of 1,1-dibromo-l-alkenes with organostannanes affords internal alkynes [24]. The (chlorocyclopropyl)dienyne side chain 84 of callipeltoside A was prepared in 95% yield by the coupling of the 1,3-dienyl-stannane 82 with the dibromide 83. The use of DMF is important [38]. 

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