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A One-Pot Sequence of Stille and Heck Couplings: Synthesis of Various 1,3,5-Hexatrienes and Their Subsequent 6π-Electrocyclizations

✍ Scribed by Paultheo von Zezschwitz; Frauke Petry; Armin de Meijere

Publisher
John Wiley and Sons
Year
2001
Tongue
English
Weight
231 KB
Volume
7
Category
Article
ISSN
0947-6539

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✦ Synopsis

Palladium-catalyzed crosscoupling reactions of 2-bromocyclohex-1-enyl triflates 7 and 11 with a variety of alkenylstannanes occurred chemoselectively at the site of the triflate leaving group to give bromobutadienes which readily underwent Heck reactions with acrylates and styrene. Both steps could be performed in the same flask to give differentially functionalized hexatrienes in up to 88 % overall yield. With simple stannanes, the same catalyst precursor could be used for both coupling steps making it possible to perform the whole sequence with only one portion of catalyst. For some of the functionally substituted stannanes, specifically adjusted catalyst systems had to be used. The 1,3,5-hexatrienes obtained were further transformed, in particular the methoxy-substituted compounds 14 a ± c were converted to bicyclo[4.4.0]decenones 30 (71 ± 97 %), bicyclo[4.3.0]nonenones 35 (74 ± 93 %), cyclodecynone 37 a (47 %), and cyclononynone 39 a (15 %). Thermal electrocyclizations of the other hexatrienes gave tetrahydronaphthalines 31 (60 ± 61 %), the tricyclic lactone 32 (72 ± 75 %) and decahydrophenanthrene 33 (75 %) in good yields.

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