2-Dehydro-2-phenylspartein

This stereochemical analysis was further confirmed by the close resemblance between the IR Bohlmatm bands of sparteine and 2-dehydro-2-phenylsparteine furthermore the IR spectrum of 14-dehydro-15-phenylsparteine showed distinguishing features in the same region, in accordance with the different orientation of the N-16 lone pair. The proposed stereochemistry is also in agreement with experimental observations that demonstrated that the 2-dehydro-2-substituted sparteine derivatives are reduced by sodiiun borohydiide via the P-plane, while 14-dehydro-15-phenylsparteine is reduced via the a-plane, which means that, in both instances, reduction takes place on the least hindered side of the corresponding iminium cations. 

Methyl-, 2-phenyl- and 2-(p-tolyl)-2-dehydrosparteine derivatives have been shown to crystallise as disalts in a transoidal arrangement, while the analogous 14-dehydro-15-phenylsparteine was curiously found to exist in a cisoidal form and to crystallise as a cisoidal monoperchlorate salt and as a transoidal dichloride di-salt. 

Fig. (29). Structures of perchlorate and hydrochloride salts of 14-dehydro-15-phenylsparteine [197]...

This effect is also observed with the derivatives 2-dehydro-2-phenyl-17p-methylsparteine and 2-dehydro-17(3-isopropyl-2--phenylsparteine which crystallise only as disalts in a mesomeric structure similar to that of their parent compounds. 

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