Sparteine crystal structure

Boche and coworkers obtained an X-ray crystal structure analysis of ( f-a-fmethylpi-valoylamino)-benzyUithium (—)-sparteine 210 . It exists even in the solid as the monomer. The sum of bond angles is 341°, which is a typical value for solvated benzyUithium derivatives. Thus, a trend towards substitution with inversion is observed. 

An X-ray crystal structure analysis was obtained from the 3-(trimethylsilyl)-aUyllithium-(—)-sparteine complex (5 )-302b. It reveals the monomeric structure of these aUyllithium compounds and a -coordination of the ally lie anion to the lithium cation. The latter is tetracoordinated and takes advantage of the chelating 0x0 group. The fixation of the lithium at the a-carbon atom is supposed to be the origin of the high regioselectivity of several substitution reactions. 

The crystal structures of lupanine (15) and its derivatives were investigated as free bases (54-56) as well as protonated forms (57-60). In all structures examined ring A was a half-chair. The conformation of ring C is a boat, and rings B and D have chair conformations. In other cases rings B, C, and D had chair conformations (54-57,59). Lupanine derivatives mamanine (16) and pohakuline (17), possible metabolites in the biosynthesis of sparteine, were studied by... 

The indenyllithium 50 is one of few stereochemically defined organolithiums whose configuration is known with absolute certainty in this case, from the X-ray crystal structure of its (-)-sparteine complex. It can therefore be shown to react with all acylating agents with retention of configuration52 (scheme 6.1.12). Only with acetone is there some loss of reg/oselectivity. 

The formation of diastereoisomerically pure complexes of 90 with (-)-sparteine is also controlled by crystallisation. Treatment of the indene 89 with BuLi and (-)-sparteine in ether gives, on warming, a yellow precipitate which reacts with carbonyl electrophiles to provide the products 91 typically with good regioselectivity and >95% ee.52 An X-ray crystal structure proved the stereochemistry of the intermediate complex to be that shown as 90b, and hence proved the stereochemical course of the substitution (see section 6.1). The complex is readily decomposed by THF, in the presence of which it rearranges to a racemic V allyllithium. 

The X-ray crystal structure of A -Boc-A -/7-methoxyphenyl-3-phenylallyI-lithium-(-)-sparteine complex has been reported [184], This structure differs from the previous structure in that the lithium is associated in an -fashion. The lithium-(-)-sparteine complex resides on the Re face of the ally unit. Stannylation of the lithium complex was established to occur with inversion of configuration. 

A crystal structure analysis of a complex between a lithiated primary carbamate and (-)-sparteine 3 unambiguously established the S configuration of this organometallic intermediate. [14]... 

Fig. 1. Molecular structures of [/-BuLi-(-)sparteine] (left), [Et20-(i-PrLi)2 (-)-sparteine] (middle) and [n-BuLi-(-)-sparteine]2 (right) in the crystal [3,5].

Optically active diamines (-)-sparteine (72) and (-)-isosparteine (73) form conqrlexes with ethylmagnesium bromide which crystallize in a form suitable for diffraction analysis. In both of these structures. 

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