Synthesis and Structure of Cyclopropano-Annelated Homosesquinorbornene Derivatives Containing Pyramidalized Double Bonds:  Evidence for the Sterical Effect of a Cyclopropyl Group on the Degree of CC Double-Bond Pyramidalization

Abstract

[reaction: see text] endo- and exo-2,3,4,7-tetrahydro-1H-1,4-methanobenzocycloheptene-7-carboxylic acid ethyl esters have been synthesized, and their Diels-Alder cycloaddition reactions with maleic anhydride, dimethyl acetylenedicarboxylate and singlet oxygen have been investigated. The X-ray analysis of four adducts indicated the pyramidalization of the central double bond. Density functional theory calculations on the isolated products and model compounds showed excellent agreement between the experimental and theoretical determined butterfly angles. Furthermore, it has been shown that a cyclopropyl group fused to [2.2.2] system decreases significantly the degree of the pyramidalization which is attributed to the steric interactions between the cyclopropyl group and ethano bridge of the norbornene systems. Due to the instability of the bicyclic endoperoxides, their X-ray analysis could not be carried out. DFT calculations on model compounds showed increased bending in the case of the product obtained by the addition of singlet oxygen to endo-2,3,4,7-tetrahydro-1H-1,4-methanobenzocycloheptene-7-carboxylic acid ethyl ester.

Noncovalent Interactions in Succinic and Maleic Anhydride Derivatives

“…We have also found several examples of derivatives of fused norbornadiene-succinic anhydride with centroid···donor distances around 2.90 Å and angles close to 90° (see examples in Figure S1). , …”

“…51 We have also found several examples of derivatives of fused norbornadienesuccinic anhydride with centroid•••donor distances around 2.90 Å and angles close to 90°(see examples in Figure S1). 52,53 To further test the directionality of the interactions we have systematically searched the CSD for short contacts (<4 Å) between the ring centroid and the donor atom (all atoms of groups 15, 16, and 17) in SA, SI, MA, and MI derivatives. The angles formed by the carbonyl C atoms, the ring centroid, and the donor atom have been also analyzed.…”

X-ray structural analyses and DFT study of 7-thianorbornenes: 4-aza-4-phenyl-10-thiatricyclo[5.2.1.0.2,6]deca-8-ene-3,5-dione and 4-aza-l,4,7-trimethyl-10-thiatricyclo[5.2.1.0.2,6]deca-8-ene-3,5-dione

“…These calculation methods give for compound 1, bond distance absolute mean deltas of 0.007, 0.005 and 0.006 Å, while maximum deltas are 0.023, 0.008 and 0.012 Å, respectively. This conclusion is somewhat surprising since the B3LYP/6-31G * approach is known to provide a reliable description of the geometry of strained polycyclic molecules [4,[24][25][26][27]. Furthermore, MP2/6-31G * calculations of dihedral angles give the best fit to experiment (compound 1, absolute mean delta is 0.382 • , while maximum delta is 0.323 • ).…”

High temperature bromination Part XXIII: Bromination of octahydro-1H-indene and octahydro-1H-4,7-methanoindene

“…This exo selectivity 38-40 is certainly not surprising since electronic factors favor attack on the convex face of the pyramidalized double bond. [41][42][43] Since the double bonds in 29 and 30 are pyramidalized, they will undergo an exo-attack by bromine radicals to form 32 and 37, respectively. The formation of the final products can be rationalized by tandem HBr elimination followed by bromine addition as depicted in Scheme 8.…”