Andrew Burritt

A NOVEL SYNTHETIC ROUTE TO 1,3-DISUBSTITUTED NAPHTHALENES

Abstract 1-(2-Substituted 1-propenyl)-2-(trifluoromethyl)benzenes are cyclized to 3-substituted 1-(4-methylpiperazino)naphthalenes in a lithium 4-methylpiperazide-mediated reaction that involves the trifluoromethyl group.

Highly regioselective hypervalent iodine mediated ring cleavage and ring expansion reactions of some pentacyclo[5.4.0.02,6.03,10.05,9]undecane derivatives

Abstract Iodosylbenzene-iodine mediated oxidative fragmentation of 3-hydroxy-4-oxa-5-methyl-hexacyclo[5.4.1.02,6-.03,10.0{5,9}.0{8,11}]dodecane (1) proceeds with regioselective C(3)-C(10) σ-bond cleavage to afford exo-10-iodo-4-oxa-5-methylpentacyclo[5.4.1.02,6.05.9.08.11]dodecan-3-one (4) in 94% yield. The corresponding reaction of 1-hydroxy-12-oxapentacyclo[5.4.1.02,6.0{3,10}.05,9]dodecane (6) proceeds with regioselective C(1)-C(11) σ-bond cleavage, thereby affording endo-9-(iodomethyl)-5-oxatetracyclo[6.3.0.02,6.03.10]undecan-4-one (9, 94% yield). Treatment of exo-8-(bromoethynyl)-endo-8-hydroxypentacyclo[5.4.1.02,6.03,10.05,9]undecane (12) with PhI(OH)(OTs)-12 resulted in highly regioselective ring expansion to afford 8-[(Z-)bromoiodomethylene]pentacycl[5.4.0.02,6.03,11.05,10]dodecan-9-one (13) as the exclusive reaction product (67% yield). The structures of 4, 9, exo-8-ethynyl-endo-8-hydroxypentacyclo[5.4.1.02,6.03,10.05,9]-undecane (11), and 13 were established unequivocally via single crystal X-ray structural analysis.

A facially dissymmetric 1,3-cyclohexadiene as a dienophile in diels-alder reactions with polyhalocyclopentadienes

Abstract Diels-Alder cycloaddition of 1,2,3,4,5,5-hexachloro- and of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene (2a and 2b, respectively) to hexacyclo[10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3, 10-dione (1) occurs in each case with highly stereoselective attack of the diene upon that face of the dienophile which is anti to the carbonyl groups. The corresponding endo,anti adduct (i. e., 6 and 8, respectively) is obtained as the exclusive cycloadduct in each case. The structures of 6 and 8 were established unequivocally via X-ray crystallographic methods. The results of AM1 semi-empirical MO calculations for cycloaddition of 1 to 2a are in accord with experiment

Bromination of exo- and endo-tricyclo[3.2.1.02,4]oct-6-ene

Abstract Bromination of exo - and endo -tricyclo[3.2.1.0 2,4 ]oct-6-ene is initiated at the double bond. This is in contrast to reaction with acid where reaction is initiated preferentially at the cyclopropane. The stationary points on the potential energy surfaces that result from bromine addition to the double bond have been identified by semi-empirical methods. The non-classical bromonium ions are predicted to be less stable than the classical structures. The exo -cyclopropylalkene gives cis and trans 1,2-dibromides along with products which result from reaction of bromine at the exo face of the alkene with subsequent rearrangement involving the C2C4 or C2C3 cyclopropyl bonds. The endo -cyclopropylalkene similarly reacts with bromine at the exo face of the alkene, but 1,2-addition does not compete with rearrangement.

ACID PROMOTED REARRANGEMENT OF PCU-DERIVED PINACOLS

Abstract Three isomerically pure pinacols, i.e., 2, 3a, and 3b, have been prepared via Na promoted reductive coupling of pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8-one (1a) and 4-spiro(cyclopropyl)-pentacyclo[5.4.0.02,6.03,10. 05,9]undecane-8-one (1b), respectively. Acid promoted pinacol rearrangement of each of these PCU-derived pinacols proceeds with exclusive migration of the C(7)C(8) σ-bond in each case, thereby affording the corresponding pinacolone (4a, 5 and 6, respectively) as the only observed rearrangement product.

Structure of the 1:1 Cycloadduct Formed via Thermal Reaction of Cyclopentadiene with Hexacyclo [10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3,10-dione

Abstract The structure of the 1:1 cycloadduct which is formed via thermal reaction of cyclopentadiene (CPD) with hexacyclo[10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3,10-dione (1) has been shown unequivocally to possess structure 3b via application of X-ray crystallographic methods. The results of semiempirical MO calculations (AM1 Hamiltonian), taken together with MMX calculational results and conclusions that arise via FMO-based arguments, suggest that electronic and steric effects each may play an important role in directing the course of the cycloaddition reactions studied herein.

NMR Study of Substituted Bicyclo[3.2.1]octanes

The 1H and 13C NMR spectra of six bromo‐ and methoxybicyclo[3.2.1]octanes were completely assigned. An axial bromine substituent at C‐2 or C‐4 results in a 5 ppm upfield shift of C‐8 due to the gauche interaction. An equatorial bromine results in an upfield shift of similar magnitude on either C‐6 (or C‐7) due to a similar gauche interaction but has little effect on the chemical shift of C‐8. The 1,4‐anti interaction of an axial bromine substituent on carbons C‐6 and/or C‐7 results in a small upfield shift (0.3 ppm) in parallel to the effect of an equatorial bromine on the chemical shift of C‐8. Similarly to the trend observed in bicyclo[2.2.1]heptanes, the substituent effects for 1,4‐gauche and 1,4‐anti interactions of the methoxy group are larger than for bromine.

Studies of proton addition to exo and endo-tricyclo[3.2.1.02,4]octane

Abstract Semiempirical methods have been used to locate the stationary points on the potential energy surface for the reaction of endoand exotricyclo[3.2.1.02.4]octanes (1) and (2) with protonated methanol. The calculations show a thermodynamic preference for rupture of the C2C4 bond. The corner transition states for cleavage of the C2C4 bonds show elongation of both the C2C4 and C2C3 cyclopropyl bonds. This is consistent with interaction of the incoming protonated methanol with both the HOMO and HOMO-1 Orbitals of the cyciopropanes. For edge attack the semiempirical transition states show elongation of the C2C4 bonds, but not of the C2C3 bonds. Mapping of the HOMO and HOMO-1 orbitals on to the electron density surface provides a simple method of predicting reaction stereochemistry.

The structure of 11,12-bis[spiro(cyclopropyl)]-1,4,4a,5,8,8a,9a,10a-octahydro-1,4:5,8-dimethano-9,10-anthraquinone

In the solid state the 2∶1 Diels-Alder adduct between spiro[4.2]hepta-1,3-diene and p-benzoquinone has a planar cyclohexadione ring with a center of symmetry. Both planar and boat conformations have been observed in similar systems, and the relative stability of the two conformers is of interest. The adduct in the gas phase should contain a mirror plane perpendicular to the cyclohexadione ring; however, a data set collected on a crystal in a capillary resulted in a structure where some bond lengths related by this mirror plane differed by more than 4σ in the solid state. Molecular mechanics, MOPAC, and the Cambridge Structural Data Base were used to investigate the factors influencing the conformation of the cyclohexadione ring and the asymmetry across the noncrystallographic mirror plane. The energy differences between the planar and nonplanar ring system is small, and the conformation is determined by crystal packing. No reason for the bond length asymmetry could be found, and a recollection of data on a crystal exposed to the environment led to a structure with statistically equivalent bond lengths.

A valence bond study of the dipole moment of CO

Abstract Valence bond calculations of the dipole moment of CO are reported. Unlike the molecular orbital approximation, the simplest valence bond wavefunction gives the correct sign for the dipole moment. The molecular orbital wavefunction is analysed using insights from the valence bond calculations. A limited configuration interaction calculation is also reported.