Experiments Towards the Formation of 1,6-Dehydroquadricyclane and Density Functional Calculations on This and Related Molecules

Abstract

1,6‐Dibromoquadricyclane (6) was obtained from norbornadiene (11) by hydroboration, oxidation of the diol 12 to the diketone 14 and its conversion into 2,6‐dibromonorbornadiene (20) using tribromodioxaphosphole 16b followed by treatment of the mixture 17/18 with potassium tert‐butoxide in DMSO and photocyclization of 20. Reaction of 6 with tBuLi (2 equiv.) led to the formation of 1‐bromo‐6‐lithioquadricyclane 7, the NMR spectra of which were observed up to 0°C. 7 did not lose LiBr to give 4, but could be trapped with H2O and chlorotrimethylsilane to give 21e (53%) and 21f (64%). Reaction of 6 with tBuLi (> 4 equiv.) gave rise to 1,6‐dilithioquadricyclane (21c), whose NMR spectra could also be recorded. 21c was converted into the corresponding 1,6‐disubstituted quadricyclanes with D2O (87%), chlorotrimethylsilane (92%), dimethyl sulfate (55%), methyl chloroformate (45%), iodine monochloride (62%), and p‐toluenesulfonyl chloride (48%). − Density functional calculations using the B3LYP‐6‐31G* level of theory showed that 1,6‐dehydroquadricyclane (4) is a local energy minimum in its singlet electronic state. 4 contains a unique structure with 4 condensed cyclopropane units. The parent hydrocarbons 27 and 28, hitherto unknown, are also local energy minima in their singlet electronic states.

Zirconium complexes bearing η5-5′,6′,7′-trihydrospiro[cycloalkane-1,4′-indenyl] ligands

“…In this way, first, spiro[5.5]undecan-1-one (1a) reacted with 2,2,2-tribromo-1,3,2-benzodioxaphosphole in CH 2 Cl 2 to form vinyl bromide 8a in 88% yield [9]. The following reaction of the organolithium reagent, obtained via a slow addition of t BuLi to 8a in THFehexanes at À80 C, with methyl vinyl ketone gave the desired divinyl carbinol 9c in only 25% yield, as the major product of this reaction was found to be spiro[5.5]undec-1-ene (Scheme 3).…”

Three-Membered-Ring-Based Molecular Architectures

“…200 1,2-Fusion of cyclopropane rings to two neighboring edges of cyclobutane formally leads to the yet elusive tricyclo-[3.1.0.0 1,3 ]hexane 265. 141 The calculated strain energy of this In contrast to this, compounds with two cyclopropane rings fused to two opposite edges of cyclobutane, that is, tricyclo-[3.1.0.0 2,4 ]hexane (anti-138), in which the SE virtually corresponds to the sum of SEs of its constituting monocycles (SE calcd ) 83.1 100 versus ∑SE cycl ) 83.2 95 ), are well-known and reasonably stable. Moreover, bridged derivatives of syn-138, namely, [3]prismane 266 201 and especially quadricyclane 267, 202 have been studied extensively.…”

“…200 1,2-Fusion of cyclopropane rings to two neighboring edges of cyclobutane formally leads to the yet elusive tricyclo-[3.1.0.0 1,3 ]hexane 265. 141 The calculated strain energy of this compound strongly exceeds the sum of SEs of the cyclobutane and the two cyclopropane rings (SE calcd ) 112.9 kcal/ mol 96 versus ∑SE cycl ) 83.2 95 ). However, the SE per carbon atom in 265 (18.8 kcal/mol) is less than that in [1.1.1]-propellane (137) (20.8 kcal/mol 98a,b ).…”

Heat of Hydrogenation of 1,5-Dehydroquadricyclane. A Computational and Experimental Study of a Highly Pyramidalized Alkene

“…7c Szeimies and co-workers have computed the relative energies of these three alkenes and their singlet-triplet splittings (∆E ST ) at both the two-configuration (TC)SCF/6-31G* 7a and B3LYP/ 6-31G* levels of theory. 9 They also calculated the olefin strain energies (OSEs) 10 of 1-4 (i.e., the differences between their heats of hydrogenation and that of a relatively unstrained reference) at the TCSCF/6-31G* level of theory. 7a thermochemical data, such as the heat of hydrogenation (∆H H2 ), have not been measured for any of these four alkenes.…”