Stille reaction double couplings

Here a Stille reaction is used to couple vinyl bromide 18 with the tin reagent 23 to yield 25 in 83 % yield. Normally, the /Z-geometry of the double bond in 23 does not switch under Stille conditions. A 5Z/5 -mixture (93 7) of 18 is coupled with pure 23 E Z 100 0) and 25 is obtained as a 75 22 3 mixture of isomers. 

Some reactions of particular interest are some examples of tandem reactions such as (i) the Stille coupling/elimination sequence with a 1,1-dibromo-l-alkene in the preparation of Callipeltoside [89] or (ii) the Stille coupling/electrocyclization cascade in the synthesis of immunosuppressants (Scheme 6.12) [90] or (iii) distan-nylated reagents such as 1,2-vinylditin and 1,4-dienyltin used in double Stille reaction sequences [91] and peculiar cascade reactions [92]. 

The Stille coupling reaction is very versatile with respect to the functionality that can be carried in both the halide and the tin reagent. Groups such as ester, nitrile, nitro, cyano, and formyl can be present, which permits applications involving masked functionality. For example, when the coupling reaction is applied to l-alkoxy-2-butenylstannanes, the double-bond shift leads to a vinyl ether that can be hydrolyzed to an aldehyde. 

Although much less common than with fully conjugated pyrimidines, cross-coupling reactions can still be performed with dihydropyrimidines, and thus the Heck reaction of the dihydropyrimidinone 518 with 4-iodoanisole 517 gave the product 519 where the double bond had migrated to the more stable 1,2-position <1996OS201>. 

In another example 2,5-bis(tributylstannyl)-furane was converted into 2,5-diarylfuranes in a double Stille coupling. Reaction with 4-bromo-benzonitrile, for example, give 2,5-bis(4 -cyanophenyl)-furane in good yield (6.31.)41... 

Choudary, B.M., Madhi, S., Chowdari, N.S., Kantam, M.L. and Sreedhar, B., Layered double hydroxide supported nanopalladium catalyst for Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes, J. Am. Chem. Soc., 2002, 124, 14127-14136. 

The intramolecular Stille coupling of tributyl(3-(2-iodobenzyloxy)prop-l-en-2-yl)stannane 572 provides 4-methyl-eneisochroman 573 in good yield, with careful control of the reaction temperature necessary to prevent isomerization of the double bond to form 4-methylisochromene (Scheme 124) <2004JOC468>. 4-Methyleneisochroman 573 can also be synthesized via an indium-mediated intramolecular cyclization of 2-bromoallyloxymethyl iodobenzene 574 in excellent yield (Scheme 124) <20050L343>. 

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