A new polymorph of N-(prop-2-ynyl)tricyclo[3.3.1.13,7]decane-1-carboxamide

The alkynyl bond of the title compound, C14H19NO, has a length of 1.170 (5) Å. The amide function shows a trans conformation with respect to the carbonyl group characterized by the torsion angle O—C—N—H of −176 (2)°. There is an intermolecular N—H⋯O hydrogen bond between the amide function and the carbonyl group. In addition, weak intermolecular hydrogen bonds stabilize the crystal structure. A comparison with a polymorphic structure shows conformational differences with regard to the orientation of the carbonyl groups with respect to the adamantyl group [O—C—C—C = 96.2 (3)° in the title compound and 123.7 (2)° in the polymorph] and the orientations of the propargyl groups in relation to the carbonyl groups [O—C—C—C = −87.7 (3) and −58.7 (2)°, respectively].

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BT2731).

Comment
Initiated by our early work on gold-catalyzed additions of nucleophiles to allenes (Hashmi et al., 2000a;Hashmi et al., 2000b) and alkynes  the investigation of the synthetic potential of propargylic carboxamides in gold-catalyzed reactions (Hashmi, 2007) revealed that they can be excellent precursors for the formation of oxazoles (Hashmi, Weyrauch, Frey & Bats, 2004) and alkylidene oxazolines (Hashmi & Rudolph et al., 2006) in highly selective reactions under mild conditions. As one of the substrates with bulky, sterically demanding substiutents which documented the broad scope of the reaction, the title compound was prepared.
The title compound ( Fig. 1) crystallizes with one molecule in the asymmetric unit of the space group Iba2. The alkynyl bond was clearly identified by the distance of 1.170 (5) Å between the carbon atoms C1 and C2. As expected, the N1-H1A amide function shows a trans conformation concerning to the carbonyl group C4=O1 indicated by the torsion angle O1-C4-N1-H1A of -176 (2)°. The crystal packing (Fig. 4) is stabilized by a number of intermolecular hydrogen bond contacts (Fig. 2). A strong intermolecular hydrogen bond works between the amide function N1-H1A as donor and the oxygen O1 of the carbonyl group as acceptor with a H1A···O1 distance of 2.16 Å and an angle N1-H1A···O1 of 161°.
The oxygen O1 of the carbonyl function is also an acceptor in more weak interactions, where the alkynyl moiety C1-H1 and the methylen group C10-H10B of the adamantyl system works as donors. The H1···O1 distance is 2.41 Å and the H10B···O1 distance is 2.57 Å respectively. The center of the alkynyl bond X1 works also as acceptor of weak hydrogen bond interactions, where the methylen group of the propargyl moiety C3-H3A and C3-H3B are the donors. The distances of H3A···X1 and H3B···X1 are both 2.93 Å. X1 is also the acceptor of an weak interaction including the methylen group C6-H6A of the adamantyl moiety with a distance H6A···X1 of 2.81 Å (see Table). Hashmi & Weyrauch et al., 2004, reported about a polymorphic structure (further abbreviated as Mol.A) of the title compound crystallized in space group C2/c, which was also crystallized by slow diffusion of petrol ether into a solution of dichloromethane. To get more insight of structural differences the carbon atoms of the adamantyl moieties of both structures were superimposed yielded in an optimal fit with a weighted r.m.s. of 0.0061 Å (

Experimental
The title compound was prepared by the reaction of adamantane-1-carboxylic acid chloride with propargyl amine in dichloromethane at 0-20 °C using a 2 mol% of 4-N,N-dimethylaminopyridine as a catalyst in 76% yield as described previously (Hashmi, Weyrauch, Frey & Bats, 2004). Crystals were grown by slow diffusion of petrol ether into a solution of dichloromethane.
supplementary materials sup-2 Refinement H atoms were located in difference fourier map, but refined with fixed individual displacement parameters [U(H) = 1.2 U eq (C)] using a riding model with C-H ranging from 0.93 to 0.98 Å. H1A of the amide function was refined free with individual displacement parameters, because of its relevance for the geometry of the hydrogen bond interaction. Fig. 1. Perspective view of the title compound with atom numbering. Displacement ellipsoids are at the 50% probability level.