Trans-enediynes

In the absence of the competing coordination with arene, the Ru- and Fe-catalyzed reactions of nonbenzannelated enediynes proceed quickly and efficiently, although photochemical liberation of the arene ligand occurs more effectively with Fe due to its lower arenophihcity relative to ruthenium (Scheme 30.18). Facile photochemical dissociation of the prodnct-metal complexes can be used for the creation of catalytic cycles. A fascinating feature of this approach is that it allows incorporation of trans/cis isomerization in the catalytic cycle. The possibihty of using trans enediynes in cycloaromatization reactions has the potential of dramatically increasing the scope of these reactions. 

A general synthetic route to p-lactam-fused enediynes (Scheme 2.321) has been successfully developed (848). When nitrone (771) was subjected to Kin-ugasa reaction conditions, two p-lactam containing products were obtained the elimination product (772) and the trans fused compound (773). 

Scheme 4. Proposed mechanism for electrochemical cis-trans isomerization of enediyne 16 [27].

A limited number of enediynes have been prepared by the reaction of copper acetylides with diiodoethylene in pyridine or DMF -For example, trans-1,6-diphenyl-3-hexcnc-l,5-diyne (52) is obtained in 90% yield when copper phenyl-acetylide (51) and r/fl j-l,2-diiodoethylene are warmed in pyridine. It was reported... 

Cao, X., Yang, Y., Wang, X. A direct route to conjugated enediynes from dipropargylic sulfones by a modified one-flask Ramberg-Backlund reaction. J. Chem. Soc., Perkin Trans. 1 2002, 2485-2489. 

Trans-enoylreductase and a- and / -ketone reduction Curacin A Biosynthesis ECH1 and ECH2 Enediyne Biosynthesis SgcE Deconstructive Analysis of PksA... 

The most interesting results in this field have been obtained with enediynes trans fused with a p-lactam. When the fusion involves carbons 3 and 4 of the latter, cycloaromatization is completely prevented, because of the rigid planar structure of the azetidinone. Several compounds of general formula 63 (r2,R = H or OH R =I1 or OR R =H, Me, SiMc2/Bu or various activating substituents), called lactenediynes , were prepared and found to be highly stable at the dry state and therefore easily manipulated (Scheme... 

A mixture of the ten-membered cyclic cw-diol 648 and its trans- om v is obtained from the enediyne dialdehyde 647. A new family of hydrocarbon rings, the three skipped cyclic C12H12 dienediynes 649 - 651, has been described. These compounds were prepared from dilithium derivatives of enediynes and diiodo- or dibromoalkenes as shown in Scheme 6. Treatment of 651 with CpCo(CO)2 gave the cobalt sandwich complex 652 ". ... 

In the resulting conjugated polymer the enediyne fragments adopt the trans configuration when the angle y between the molecular axis and the stacking axis is approximately 45° and the distance d is less than 430 pm [16] (Scheme 7.1). 

The cobalt-catalyzed [2+2+2] cycloaddition of 4-hydroxy-substituted enediynes [152] that has been implemented in the synthesis of 2-hydroxy substituted decahydrophenanthrenes [153] has shown that the hydroxy group in the propargyl position tolerates the chosen reaction conditions. So, this approach could be an appropriate route to hydrogenated trans-phenanthrenes, which are the ABC cores of ergosterin and lumisterin steroids. This was a reason to consider the diastereoselective synthesis of (3S)-hydroxyandrosta-5,7-diene-17-ones 2.307, the precursors of vitamin D, via a D ABCD approach. 

The bipyridyl group in bipyridyl enediyne 3.882 exists in the tran-soid conformation, where the atoms of the terminal acetylenic branches are separated from each other. After reaction with the metal ion to produce the chelate 3.883 the ligand adopts a cisoid conformation (Scheme 3.121[24a]). 

Konig, B., Schofield, E., Bubenitschek, P. and Jones, P.G. (1994) Synthesis and photoinduced cis-trans isomerization of diaryl enediyne chromophores. Journal of Organic Chemistry, 59(23), 7142-7143. 

---