Selective cross Diels-Alder reactions of 2-(phenylsulfonyl) 1,3-dienes

Ruthenium‐Catalyzed Cascade Reactions of Diynes with Norbornadiene – Synthesis of Norbornene Derivatives

“…Additionally, 7a contains six stereogenic centers and should be difficult to be produced by other synthetic methods. For example, the generation of 7a by a DielsAlder reaction [18,19] of diene 14 [20] with NBD is inefficient.…”

Unravelling the Synthesis and Chemistry of Stable, Acyclic, and Double‐Deficient 1,3‐Butadienes: An endo‐Selective Diels–Alder Route to Hedgehog Pathway Inhibitors

“…Although cyclic electron‐deficient dienes ( 3 , Scheme ) are relatively stable and have marked their presence in the organic chemistry literature; acyclic, stable, and electron‐poor butadienes ( 2 ) remain largely inaccessible, despite the dedicated efforts from some groups in the last quarter of twentieth century. McIntosh, Bäckvall and Spino's groups synthesized and explored the dienes 4 (Figure ) bearing only one electron‐withdrawing group in the Diels–Alder cycloaddition reactions . However, these dienes were prone to nucleophilic additions and undesired dimeric cycloadditions .…”

“…Here, we report af acile syn-thesiso fe lectron-deficient, acyclic, ands table 1,3-butadienes and unravel their intriguing cycloaddition chemistry affording new carbo-a nd heterocyclic small molecules, which led to the discoveryo fanew class of small-molecule inhibitors of Hedgehog signaling pathway.Although cyclic electron-deficient dienes [8] (3,S cheme 1) are relativelys table and have marked their presence in the organic chemistry literature; [9] acyclic,s table, and electron-poorb utadienes( 2)remainlargely inaccessible, despitet he dedicated efforts from some groups in the last quarter of twentieth century.M cIntosh, [10] Bäckvall [11] and Spino's [12] groups synthesized and explored the dienes 4 ( Figure 1) bearing only one electron-withdrawing group in the Diels-Alder cycloaddition reactions. [13] However,t hese dienes were prone to nucleophilic additionsa nd undesired dimericc ycloadditions. [11a, 14] In particular, dienesw itha ne ster moiety had to be generated in situ for any further transformation.…”

“…[11a, 14] In particular, dienesw itha ne ster moiety had to be generated in situ for any further transformation. [13,15] In successful cases,b oth electron-rich and -poor olefins reacted with dienes 4 to produce Diels-Alder adducts. [16] Diene 5 with 1,2-dicarbonyl functions also showeds imilar limitations and displayed ar elativelyl esser dienicc haracter.P adwa et al developedamultistep synthesis of 2,4-bis-sulfonyl 1,3-butadienes (6,F igure 1).…”

“…[22] Both 13 a and 13'a were stable at room temperature [Scheme 3, reactions (i)a nd (ix) and Supporting Information] in DCE even at higher temperature [reactions (iii)a nd (x)].A t highert emperature in toluene[ microwave (MW) irradiation, 200 8C],d iene E,E-13 a remained stable with slight conversion to 13'a [reaction (ii)],h owever,t he latter isomerized to 13 a and also displayed dimerization and decomposition (see Supporting Information). Interestingly,i n[ D 6 ]DMSO,b oth the two dienes reached ar atio of about6 0:40 in favor of E,E-13 a [reactions (iv) and (xi)].I nt he presence of catalytic triphenylphosphine and at high temperature,b oth dienes 13 a and 13'a acquiredaratio of 74:26 with Z,E-13'a as the minor isomer [Scheme3,r eactions (v) and (vii)].I ntriguingly,t he phosphinemediated conversiono fZ,E-13'a at room temperature deliv-Scheme2.a) An attempted transformation of allene 7 into diene 9;b )proposed isomerizationo fa,g-disubstituted alleneesters (10)into dienes (13). Table 1.…”