Brian Halton

A Variant of Peterson Olefination: Nitrophenyl-Substituted Methylenecyclopropa[b]naphthalenes

The successful use of a gem-disilyl compound in Peterson olefination with nitrosubstituted aromatic aldehydes and ketones is achieved for 1,1-bis( trimethylsilyl )-1H-cyclopropa[b]naphthalene (9) by employing potassium fluoride in acetonitrile and using a catalytic quantity of tetrabutylammonium fluoride as the fluoride ion transfer agent.

SCC-EH Molecular orbital calculations of the election distribution in benzocyclopropene and its cation, anion and radical

Abstract The SCC-EH MO method is applied to benzocyclopropene and its as yet unknown cation, anion and radical. The π-electron distribution of the neutral molecule reflects the particular geometry assumed, but the total energy is relatively insensitive to small geometric changes. Significant stabilisation of the ions is predicted to occur by charge delocalisation with the free radical having a stability intermediate to the cation and anion.

Bicyclo[3.10]Hex. I(6)-enes: Reactivity of the 3-oxa derivative

Abstract Treatment of the dihalo-3-oxabicyclohexane 1 with excess t-butoxide leads to the ring strained cyclopropene 3 . This is captured by diphenylisobenzofuran as Diels-Alder adduct 7 , whereas with furan only the ring expanded vinylcarbene 9 is intercepted and spirocycle 11 results.

Competitive pathways in the synthesis of cyclopropa[b]naphthalene

Abstract The product distribution obtained from dehydrochlorination of the benzobicycloheptene 1 is dependent on the reaction conditions. In tetrahydrofuran at high base concentration cyclopropa[b]naphthalene (2) predominates, whereas at low base concentration 6 - chlorobenzo[a]cyclohepta - 1,3,5 - triene (4) is the major product. In dimethyl sulphoxide 2 and 4 are formed in low yields, the ether 10 being the major product.

Studies in the cycloproparene series: Reactions of alkylidenecycloproparenes with electrophiles

The addition of an electrophile to the alkylidenecycloproparenes (2a-d) is dominated by capture at the exocyclic centre with formation of the corresponding cycloproparenyl cation, e.g. (15). Subsequent reaction with the counter ion is usually accompanied by cleavage of the three-membered ring. Thus compounds (2) give the ethanones (4) with aqueous acids whilst anhydrous acetic acid yields the vinyl acetates (5). Silver(1)-catalysed methanolysis of (2) leads to vinyl ethers (6); the alkyne (7) is formed only from (2d) which carries a vinylic proton. Brominations and bromine water additions lead to products of ring expansion (8)-(10) or ring cleavage (11)-(14) depending upon the conditions employed. These latter reactions demonstrate a delicate balance between cycloproparenylcarbinyl cation formation and cleavage of the three-membered ring.

1,3-Diradical intermediates in 3H-pyrazole photolyses: 1,4 addition to dienes

Abstract The photolyses of pyrazolopyridazines (2a-c) lead to alkenes (4a-c). With added methanol, furan or buta-1,3-diene, intermediates (3a-c) are trapped as compounds (6a-c)–(8a-c) respectively.

Studies in the cycloproparene series: chemistry of 1-acyl-1H-cyclopropa[b]naphthalenes and synthesis of cyclopropa[b]naphthalenylidene enol ethers

Abstract The 1H-cyclopropa[b]naphthalenyl anion reacts with N,N-dimethylamides to provide C-1 acyl derivatives in good yield in what are rare examples of mono-substitution in the cycloproparene series. The availability of these acylcycloproparenes provides for subsequent benzylic proton abstraction and enolate ion interception to give O-silyl and O-phosphinate derivatives. This reaction sequence leads to the first cyclopropa[b]naphthalenylidene enol ethers and provides the only example of exocyclic alkene formation taking place in one step from the benzylic centre. Protonation of the acyl derivatives by mineral acid triggers three-membered ring opening to 2,3-disubstituted naphthalenes rather than 2-monosubstituted analogues that typically arise from protonation at the aromatic ring. Upon thermolysis ring expansion to a naphthofuran occurs.

Competitive pathways in the dehydrochlorination route to cyclopropa-arenes

Abstract The dehydrochlorination route to cyclopropabenzene 4 from 2 yields t-butoxymethylbenzene 8 as the sole isolable by-product. The path by which the majority of 8 is produced does not involve solvolysis of 4. The analogous route to cyclopropa[b]naphthalene 3 has been re-examined and the previously proposed 6-chlorobenzo[a]cyclohepta-1,3,5-triene 10 and 2-(t-butoxymethyl)naphthalene 9 have been reassigned as 1-(chloromethyl)naphthalene 5 and 1-(t-butoxymethyl)naphthalene 7, respectively. Evidence is presented which supports the presence of competing pathways in both dehydrochlorination processes.

The preparation of exocyclic functionalised alkylidenecycloproparanes via a new procedure

Abstract The general preparation of several new alkylidenecycloproparenes containing functional groups at the exocyclic (C8) position is described.

The formation and decomposition of 1,1-dichloro-1H-cyclopropa[l]phenanthrene

Abstract Selenoxide elimination from (8) delivers 1,1-dichloro-1H-Cyclopropa[l]-phenanthrene (9) which is converted into the ester (11) upon reaction with methanol.The intervention of (9) is supported by labelling studies.