Heteroannular conjugated diene

In steroid systems, the homoannular diene in ring A and the heteroannular diene in AB rings are generated. The allylic 3a-carbonate 514 affords the homoannular conjugated diene 515 as a main product and a small amount of the heteroannular diene 516. On the other hand, the heteroannular conjugated diene 516 is obtained exclusively from 33-carbonates 517. The elimination reaction proceeds smoothly at room temperature. 

Hetero- or homoannular conjugated dienes are prepared in hydronaphthalene derivatives by the Pd-catalyzed regioselective elimination of allylic carbonates under mild conditions. The heteroannular conjugated diene 496 was obtained selectively by the Pd-catalyzed regioselective elimination of the -oriented allylic carbonate 494 under mild conditions via the stable intermediate 495. The homoan-... 

The reaction has been applied successfully to the synthesis of a precursor of provitamin D. 520, which has a homoannular conjugated diene in the B ring[340]. Treatment of the 7a-carbonate 518 with Pd cataJy.st at 40 C afforded the 5.7-diene 520 regioselcctively in good yield. No heteroannular diene 521... 

The ultraviolet spectra of crowded olefins and substituted butadienes have been studied the sign of the Cotton effect has been related to the chirality of a series of w-molecular complexes of olefins with tetracyanoethylene the sign of the chiral-optical effects of non-planar heteroannular cisoid dienes is opposite to that predicted from the diene rule. Studies of linear and circular dichroism in mono-olefins and magnetic circular dichroism of conjugated olefins have been made, and the experimental ionization potentials of fourteen alkenes have been correlated with the inductive effects of substituents. ... 

The base Amax value for the former is taken as 214 nm and for the latter as 253 nm. To these values are added increments according to the nature of the substituent present and other structural features as shown in the table. In those cases where homoannular and heteroannular chromophores coexist in conjugation, the base value for the homoannular contribution is used, to which is added the appropriate increment for extended conjugation. It should also be noted that homoannular dienes in ring systems other than the six-membered ring do not give a satisfactory correlation between calculated and experimentally determined Amax values. The rules however are adequate for acyclic or heteroannular... 

A heteroannular diene is a conjugated system in which the two double bonds belong to two different rings. However, these double bonds are also exocyclic, one of them being exo-to ring A and the other exo-to ring B. 

Parent heteroannular diene Double bond extending the conjugation Alkyl substituent or ring residue Exocyclic location of double bond to any ring Groups OAc, OR... 

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