On the Absolute Configuration of Indane‐1‐carboxylic Acid

Abstract

Summary Doubts that have recently been expressed [ l ] about the currently accepted (+ )-(R), (-)-(S)[2] absolute configuration of indane-1-carboxylic acid appear to be unwarranted. Our In the case of indanes the conformational relationship between the aromatic ring and a substituent on the five-membered ring is fairly well-defined'); this makes indanes valuable in areas of research where such relationships matter. As seen in Schemes l a , l b , and 2, indane-1-carboxylic acid (1) occupies a central position, rather like the hub of a wheel, in the pattern of configurational correlations in this series. It is important, then, to attribute neither more, nor less, certainty to the currently accepted configuration (+ )-(R), (-)-(S) [2] for 1 than the available evidence warrants. For this reason we cannot let certain statements made recently in this journal [ 11 stand unchallenged. Specifically, and to quote: 'It is shown unequivocally by chemical correlations and Raman optical activity spectra that the @)-configuration has to be attributed to (+ )-1-methylindane I )Some flexing of the saturated ring is possible but it seems likely that there is only one conformational energy minimum; the extent of noncoplananty could be a function of the steric requirements of the substituents. Puckering has been explicitly invoked by several workers in efforts to account for chiroptical phenomena that seem difficult to explain otherwise [7] [8] [9] [ 111 [ 151.

On the Absolute Configuration of (+)‐Indane‐1‐carboxylic Acid

“…Thus, the absolute configuration of (+)-I is well-established and in connection with the information collected in the foregoing paper of Brewster [3], and in the Atlas of Stereochemistry [ 121, no contradictions are left with respect to it. This means that in our statement in [5] "that the fS)-configuration has to be attributed to (-)-1-methylindane ((-)-4)7 as well as to (+)-15), provided there is no trivial mistake in Brewster & Buta's work" [2], only the second possibility remains.…”

“…curve of optically active 1-methylindane ( Fig. 1) which was unfortunately not noticed in all cases led to further confusions (see [15] and literature cited in [3] and [5]). The chirally perturbed indane system therefore appears susceptible to solvent effects possibly due to a shift in the conformational equilibrium between a pseudoaxial and a pseudoequatorial position of the methyl group.…”

“…To 7.5 g (0.039 moi) (-)- 3 [24] 18 ml fluorosulfonic acid was carefully added. After stirring for 1 h at 50" and for an additional h at 20" the mixture was poured to 50 ml icelwater.…”

Asymmetric Cyclization of Achiral Olefinic Organolithiums Controlled by a Stereogenic Lithium: Intramolecular Carbolithiation in the Presence of (−)-Sparteine

“…For this reason, it was necessary to allow solutions of 8 in n -pentane−diethyl ether containing 2.2 equiv of (−)-sparteine to stand for 1 h at +22 °C to effect cyclization. Nonetheless, even at this relatively high temperature, the cycloisomerization of 8 in the presence of 1 is fairly enantioselective: as illustrated in Scheme , trapping of the (1-indanyl)methyllithium product by protonation gave a 76% yield of the known ( S )-(−)-1-methylindan ( 9 ) in 76% yield with an ee of 42%.

2

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