ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Sodium [1,3-13C2]cyclopentadienide in tetrahydrofuran (THF) has been prepared from the corresponding labelled [13C2]cyclopentadiene which was synthesized from 13CO2 and (chloromethyl)trimethylsilane (cf. Scheme 10) according to an established procedure. It could be shown that the acetate pyrolysis of cis-cyclopentane-1,2-diyl diacetate (cis-22) at 550 ± 5° under reduced pressure (60 Torr) gives five times as much cyclopentadiene as trans-22. The reaction of sodium [1,3-13C2]cyclopentadienide with 2,4,6-trimethylpyrylium tetrafluoroborate in THF leads to the formation of the statistically expected 2:2:1 mixture of 4,6,8-trimethyl[1,3a-13C2], -[2,3a-13C2]-, and -[1,3-13C2]azulene (20; cf. Scheme 7 and Fig. 1). Formylation and reduction of the 2:2:1 mixture [13C2]-20 results in the formation of a 1:1:1:1:1 mixture of 1,4,6,8-tetramethyl[1,3-13C2]-, -[1,3a-13C2]-, -[2,3a-13C2]-, -[2,8a-13C2]-, and -[3,8a-13C2]azulene (5; cf. Scheme 8 and Fig. 2). The measured 2J(13C, 13C) values of [13C2]-20 and [13C2]-5 are listed in Tables 1 and 2. Thermal reaction of the 1:1:1:1:1 mixture [13C2]-5 with the four-fold amount of dimethyl acetylenedicarboxylate (ADM) at 200° in tetralin (cf. Scheme 2) gave 5,6,8,10-tetramethyl-[13C2]heptalene-1,2-dicarboxylate ([13C2]-6a; 22%), its double-bond-shifted (DBS) isomer [13C2]-6b (19%), and the corresponding azulene-1,2-dicarboxylate 7 (18%). The isotopically isomeric mixture of [13C2]-6a showed no 1J(13C,13C) at C(5) (cf. Fig. 3). This finding is in agreement with the fact that the expected primary tricyclic intermediate [7,11-13C2]-8 exhibits at 200° in tetralin only cleavage of the C(1)—C(10) bond and formation of a C(7)—C(10) bond (cf. Schemes 6 and 9), but no cleavage of the C(1)—C(11) bond and formation of a C(7)—C(11) bond. The limits of detection of the applied method is ≥96% for the observed process, i.e., [1,3a-13C2]- 5 + ADM→ [7,11-13C2]-8→[1,6-13C2]-9 →[5,10a-13C2]-6a (cf. Scheme 6).
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19950780604
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