Absolute Conguration And Tautomeric Structure Of Xylindein (Page 2 of 4) in pdf

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Edwards and Kale (Fig. 1). The resulting dimethylxy-

lindein (2), which is soluble in various organic solvents,

was subjected to the hydrogenation conditions. The

reaction mixture was rapidly ®ltered through Celite, and

then the resulting dihydro derivative 3 was exposed to

alkylation using -bromobenzyl bromide and sodium

hydride in DMF to give dihydrotetraalkylxylindein (4).

The bromobenzyl derivative 4 was recrystallized from a

mixture of 2-butanol and chloroform to give red needles

which were not suitable for X-ray analysis. Next, crys-

tallization was performed with hot 80% aqueous phenol

to give red plates which were subjected to single-crystal

X-ray di€raction analysis. The absolute con®gurations

of both chiral centers of 4 were assigned as

. This

Fig. 2. A stereoview of compound 4

4PhOH.

crystal contains one molecule of 4 and four molecules of

phenol per asymmetric unit (Fig. 2).

Although the absolute con®guration of xylindein (1),

which had been unknown for a long time, was deter-

mined at this time by X-ray crystallographic analysis of

its derivative 4, ambiguity about the xylindein tautomeric

structure still remains. X-ray crystallographic analysis of 1

would serve to elucidate this problem. The crystals for X-

Fig. 3. A stereoview of compound 1

4PhOH.

ray analysis of 1 were prepared according to the method

hydroxy groups (1.382 and 1.358 A Ê ) are shorter com-

of Edwards and Kale (1965) (recrystallized from hot 80%

pared to the standard geometries (CˆO: 1.22A Ê , CÀO:

aqueous phenol) to give magenta plates. The crystals

1.43 A Ê , Hendrickson et al., 1970). Nevertheless, these

obtained were analyzed by X-ray crystallography with-

out washing with organic solvent, because washing with

data support that the represented tautomer is the proper

EtOH resulted in damaging the crystal structure,

one among the possible tautomers in the crystal state.

removing phenols contained in the crystal and produ-

cing an amorphous solid. Also in this case, this crystal

contains one molecule of 1 and four molecules of phenol

3. Experimental

per asymmetric unit (Fig. 3). The structure is not sym-

metrical when comparing the top and bottom halves.

Accordingly, the bond lengths of the corresponding

groups are not the same, which should be derived from

Melting points are uncorrected. Optical rotations

the coordination e€ects of the phenols. Di€erent coor-

were measured on a JASCO DIP-360 polarimeter. UV

dination modes of two phenol moieties should bring

spectra were recorded on a HITACHI U-2001 spectro-

about the extended and the shortened carbonyl bond

meter. IR spectra were recorded on a JASCO FT-IR-

lengths of the two lactone groups (1.179 and 1.311 A Ê ).

200 spectrometer as a KBr pellet or on an NaCl cell

The bond lengths of the two quinone carbonyl groups

with nujol.

H and

C NMR spectra were recorded on

(1.291 and 1.318 A Ê ) are rather long and those of the two

a JEOL Lambda-300 (300 and 75 MHz, respectively)

Fig. 1. Chemical conversions of xylindein (1) to a bromobenzyl derivative 4.

Absolute Conguration And Tautomeric Structure Of Xylindein Page 2

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