Diene synthesis scission

Ansa-steroids s. 40, 494 one-pot diene synthesis-retrodiene scission s. Ann. Chem. 1987, 1095 application to the preparation of macrolides s. Heterocycles 28, 333-46 (1989). 

Crombie and Rainbow reported synthesis of terminal dienes of high. E-selectivity via samarium diiodide mediated scission of 2-vinyl-3-chlorotetrahydrofuran (equation 175) or the corresponding pyran derivatives296. Interestingly, both cis- and frans-2-substituted 3-chlorotetrahydrofurans give the same diene, indicating the involvement of identical intermediates formed by electron transfer from samarium diiodide. 

Tetrahydropyrrolizines (210) and (211) can be formed via radical scission of either bond a or b in the intermediate vinyl-aziridine (208) but yields are moderate at best and the major product is the monocyclic pyrroline (209), formed by a 1,5-homo-dienyl rearrangement. The route therefore could provide a useful access to the pyrrolizidine framework if conditions could be identified which would allow more controlled and efficient breakdown of (208). The synthesis of substitute pyrrolines by ring expansion of vinyl aziridine derivatives has also been accomplished in a palladium-catalysed reaction. N -Tosyl-2-vinyl five- and six-membered nitrogen heterocycles (213) ace obtained in generally high yields under mild conditions from precursor dienyl nitrogen heterocycles (212) in the presence of a catalytic amount of [Pd(PPh ) ]. The complete diene unit is required for the... 

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