The stereoselective synthesis ofesters 5% 6, 7, 8, 12b, 12$ and 13 and dicarboxylic acids 5, 12, and 12a by KMn04 oxidation, and, in the case of esters, dkomethane esterification, of the known tricyclic ketones 1, 2,3, and 4 or their derivatives 9, 9a, 9b, 10, 10% 11, and lla, is described. Conformational analyses of these compounds have been carried out by 200-MHz 'H-NMR and "C-NMR spectroscopy at room temperature with the aid of theoretical calculations (MM2 program). Also, a 'H-NMR study of compound Sa at temperatures between 21 and 119°C is presented. In general, a good agreement has been found among ex- of the exo-3-H/syn-9-H interaction in the boat-chair conformation of bicyclo[3.3.l]nonan-9-one is responsible for the greater population of this conformation in this compound ( 2 2 O / 0 ) '~) with respect to the bicyclo[3.3.l]nonane (5 f 4%)9). An exo-2 substituent such as CI or OH does not change the preference of the system for the chair-chair conformation4). However, one endo-3 substituent makes the boat-chair conformation, in which this substituent is equatorial, the preferred one2-8.'2'. Much attention has been paid also to the conformational analysis of 3-heterobicylo[3.3.1]nonane derivatives (3-oxa derivatives 17) and specially 3-aza derivatives in which the chair-chair conformation lacks the endo-3-Hlendo-7-H interaction. Less attention has received the conformational analysis of bicyclo[3.2.l]octane derivative~'~.*~), in which the preferred conformation with a chair cyclohexane ring does not show severe destabilizing H/H interactions.Some time ago, we established 13) that exo-2,exo-4-dimethoxybicyclo[3.3.l]nonan-9-one exists preferentially in a chair-chair conChem. Ber.
A short synthesis of the titled compound, a possible intermediate to prepare dodecahedrane, whose key-steps are the stereoselective trimethylene-annelation in the C2 and C3 positions of dimethyl 7,7-diethoxynorbornane-2,3-dicarboxylate and the high-yield intramolecular C–H insertion of a carbene generated from a 10-oxotricyclo[5.2.1.02.6]decane derivative, is described.
A synthesis of dimethyl tetracyclo(5.2. I .02~h.0".x]decane-7,8-dicarboxylate, 3, whose key step implies the formation of the CI-C2 bond by regioselective intramolecular C-H insertion of a carbene generated from dimethyl (lR,2S,6R,7S)-lOoxotricyclo[5.2.1 .0'~6]decane-2,6-dicarboxylate, 1 via its tosylhydrazone, is described. Attempts to synthesize diester 3 or compounds containing its carbon skeleton, by forming the same C-C bond, starting from dimethyl (lR,2R,6S,7S)-4- (1) and its methyl (2) and 1,16-dimethyl derivatives (3), the first compounds containing such a type of carbocyclic skeleton. The synthesis of dodecahedrane, however, implies 23 consecutive steps from cyclopentadiene, the overall yield being in the range of 0.1%, which limits its supply. Consequently it is still a challenge to obtain it through a shorter and higher yielding sequence (4).As part of our contribution to polyquinane chemistry (5-7), we describe herein the studies that have led to the successful synthesis of dimethyl tetracyclo[5.2. 1.0"6.03.8]decane-7,8-dicarboxylate, 3, a possible intermediate for a convergent synthesis of dodecahedrane.The retrosynthetic analysis of diester 3 shows that cleavage of the strategic (8) C1-C2 bond gives the well-known tricyclo[5.2.1 .02.6]decane skeleton, in contrast with other cleavages, which give precursors that are not easily accessible. Since the C1 and C2 atoms and their neighbours in compound 3 have no functionality, intramolecular C-H insertion of a carbene was considered to be the reaction of choice to form the 'Author to whom correspondence may be addressed. C 1-C2 bond. As shown in Scheme 1, there exist two ways to carry out such a transformation, depending on the carbon atom at which the carbene is generated. In fact, Neff and Nordlander (9) had utilized the first way in order to synthesize tetracyclo-[5.2.1 .02,6.03*8]decane from tricyclo[5.2.1 .02,6]decan-1 0-one.Because the synthesis of dimethyl (1 R,2R,6S,7S)-4-oxotricyclo[5.2.1 .02s6]decane-2,6-dicarboxylate, 2, appeared to be easier (5) than that of dimethyl (1 R,2S,6R,7S)-1O-oxotricyclo-[5.2. l.02~6]decane-2,6-dicarboxylate, 1, and because we were looking for a new entry into this carbocyclic skeleton (9, lo), we undertook the preparation of ketodiester 2 through the sequence depicted in Scheme 2.The starting product for this synthesis was bicyclo[2.2.1]-hept-2-ene-2,3-dicarboxylic anhydride, 4 (1 1). Reaction of anhydride 4 with excess butadiene gave (1 R,2R,7S,8S)-tricyclo[6.2.1 .0'~7]undec-4-ene-2,7-dicarboxylic anhydride, 5, in 81% yield. This compound had been previously prepared by Alder and Backendorf (l2), but its configuration was not established. However, owing to the fact that reaction of bicyclo-[2.2.l]hepta-2,5-diene-2,3-dicarboxylic anhydride with butadiene (13) gives a 1 : 1 mixture of the endo and exo adducts, it seems reasonable that anhydride 4, with the C4-C5 bond Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.212.246.108 on 05/10/18For personal use only.
The conformational analysis of several 2,4-disubstituted 9-oxobicyclo[3.3.1]nonane derivatives (diesters IIIb and IIIc, and dihalo compounds IV, Va, Vb and VI) derived from 9-oxobicyclo[3.3.1]nonane-exo-2, exo-4-dicarboxylic acid has been studied by 1H and 13C NMR spectroscopy with the aid of Molecular Mechanics Calculations (MM3 program).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.