Directed Synthesis of Rotaxanes

16 Directed Synthesis of Rotaxanes Investigations of the directed synthesis of rotaxanes were carried out by Schill and Zollenkopf.25,26 Bifunctional diansa compound 449, whose synthesis was already described in Section 9.6.2, was used to alkylate the sodium salt of 7V-acetyl-2,4,6-tri-/?-tolylaniline in dimethylformamide to give compound 576 in 81 % yield. Confirmation of the assumed structure was obtained by mass spectrometry. It is remarkable that the spectrum showed the molecular ion peak at m/e =1611 with the relative high intensity of 27 % of the base peak. The conversion of prerotaxane 576 to a rotaxane was carried out in analogy to the synthesis of catenanes.16 Ketal cleavage with hydrobromic acid in acetic acid gave aminocatechol 577 and partially deacetylated products. The reaction mixture was then dehydrogenated with ferric sulfate to the amino-tf-benzoquinone. Through acid hydrolysis the corresponding hydroxy-ö-benzoquinone is formed; it spontaneously tautomerizes to the /7-quinoid structure 578. Besides the compounds 577 and 578, the reaction mixture also contained the partially deacetylated derivatives. Acetylation of the reaction mixture resulted in tetraacetate 579 from which the hexaacetate 580 was prepared by reductive acetylation: The following arguments in favor of the assumed rotaxane structure 580 were brought forward : 1. The elemental analysis is satisfactory. 2. The IR spectrum shows the expected bands. The spectra of the rotaxane and the equimolar mixture of the two single components are identical except for one weak additional band in the mixture. 151

152

1 6 . DIRECTED SYNTHESIS OF ROTAXANES

,(CH2)

'(CH2)!

(CH 2 ) 12 -R

->oç

HO

I

HO (CH 2 ) 12 -R 449: R = Br 576: R = Z ,(CH2)

-(CH2)12

,(CH 2 ) 12 -Z

(CH 2 ) 12 ^

y

N -~-_(CH2)l2_Z

577 (CH 2 ) 12 -Z

(CH 2 ) 12 -Z 578: R = H 579: R = COCH3 -(CH2) (CH 2 ) 12 -Z

H,C

153

16.1. SYNTHESIS OF SUBUNITS OF ROTAXANES

3. In thin-layer chromatograms the rotaxane is homogenous and has a Rf value clearly different from the Rf values of its individual components.

16.1. Synthesis of Molecular Subunits of Rotaxanes The synthesis of the macroheterocycle 390b has already been discussed in Sections 9.4.2 and 9.8. For the synthesis of the dumbbell-shaped comH

/°-^V- ( C H 2 ) l 2 -° R

r

H5C2^

581: 582: 583: 584: 585:

R R R R R

= = = = =

(CH2)12-OR R' = H COCH 3 ;R' = H COCH 3 ;R' = N 0 2 H;R=N02 H ; R ' = NH 2

HA 586: 587: 588: 589: 590: 591:

vTY R= R= R= R= R= R=

(CH2),2 R _^ao

"

1 AÎ-C4H9 (CH2)12-R OH;R' = H O H ; R ' = w-C4H9 OCOCH 3 ;R' = /i-C 4 H 9 OCOCH 3 ; R' = COCH 3 Br;R' = w-C4H9 Z;R=rt-C4H9 CH 3

H3C

H3C

/%.(CH2)12-Z

RCT (CH2)12-Z 592: R = H ; R ' = N ( / Î - C 4 H 9 ) 2 593: R == C O C H 3 ; R = O C O C H 3

154

1 6 . DIRECTED SYNTHESIS OF ROTAXANES

ponent 593, catecholdiol 433 (see Section 9.5) was ketalized with diethyl ketone to 581, acetylated to 582, and nitrated in the 5-position with cupric nitrate in acetic anhydride109 to 583. Hydrolysis led to diol 584 which was converted to amine 585 by catalytic reduction. The alkylation with butyl bromide was carried out in refluxing isoamyl alcohol in the presence of potassium carbonate and sodium iodide. Even though an excess of alkyl bromide was used, only a mixture of mono- and dialkylamino compounds 586 and 587 was obtained. The former predominated in this mixture. After acetylation, the tertiary amine 588 could be separated from amide 589. Saponification of 588 led to diol 587 which was converted with triphenylphosphine dibromide193 to dibromide 590 in 25% yield. Reaction with the bulky end groups gave 591, subsequent ketal cleavage led to the catechol derivative 592 which was converted, in analogy to the rotaxane, to pentaacetate 593.