Cycloallenes. Part 15: 1 3 δ 2 -1 H -Naphthalene (2,3-Didehydro-1,2-dihydronaphthalene) from 3-Bromo-1,2-dihydronaphthalene

Computational Assessment of the Electronic Structure of 1‐Azacyclohexa‐2,3,5‐triene (3δ2‐1H‐Pyridine) and Its Benzo Derivative (3δ2‐1H‐Quinoline) as well as Generation and Interception of 1‐Methyl‐3δ2‐1H‐quinoline

“…Six-membered cyclic allenes that definitely or presumably have a chiral ground state are attacked by nucleophiles at the central carbon atom of the allene moiety: cyclohexa-1,2-diene, 1,1-dimethyl-3d 2 -1H-naphthalene [1] (1, R C 6 H 5 ), [3a] 1-oxacyclohexa-3,4-diene [16] and 3d 2 -1H-naphthalene. [17] However, if the ground state is zwitterionic, as calculations demonstrate for 14 in solution, that is 14 b, [9] or if the zwitterionic state is only a few kcal mol À1 less stable than the chiral state, as in the case of 12 (energy difference of 3.2 kcal mol À1 in solution), [9] KOtBu interacts with an allene terminus exclusively (Scheme 2). This is readily explained since these steps can be considered as an addition to a quasicarbonyl group (12 b) and as conjugated addition to an a,bunsaturated quasi-carbonyl compound (14 b).…”

“…[9] Both species can be trapped by activated olefins with formation of cycloadducts, [35] even in the presence of KOtBu. [17,36] Although the zwitterionic state (12 b) of the chromene 12 approaches the allene form (12 a) to within a few kcal mol À1 , [9] the formation of cycloadducts is still the major process, in spite of the presence of KOtBu. [10] However, the pyran 14 [9] and the quinoline 7 do not furnish any cycloadducts but only products resulting from the interception by KOtBu.…”

“…If the reaction was performed in [D 8 ]THF and the mixture was immediately analysed by NMR spectroscopy, 2-tert-butoxy-1-methyl-1,2-dihydroquinoline (17) was shown to be the precursor of 10 and 11. The structure of 17 is evidence for the title cycloallene 7, which arises from 9 by b elimination of hydrogen bromide and is trapped by KOtBu to give 17 so fast that cycloadditions of 7 with furan or styrene cannot compete.…”

1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

“…Our contributions to the field of six-membered cycloallenes have the principal goal of trapping species with a fleeting existence with activated olefins, thus giving cycloadducts; their main results have been summarized in two reviews. [1,2] In two more recent studies, we have investigated reactions undergone by cyclohexa-1,2,4-triene [6] and 3δ 2 -1H-naphthalene [7] in addition to cycloadditions with activated olefins. [8] The symmetrical (1) [9] and the unsymmetrical isopyran (2) [10Ϫ12] (Scheme 1) have been generated and characterised by trapping products.…”

Incorporation of an Allene Unit intoα-Pinenevia β-Elimination

“…Furthermore, deprotonation of 7 by the strong base might also generate the allylic anion 14, which can take up H + to form the conjugated diene 12. Recently, Christl et al [14] reacted the allene precursor 3-bromo-1,2-dihydronaphthalene (and derivatives thereof) with t-BuOK and obtained a mixture of naphthalene and enol ether as the major products. The formation of the major product was also rationalized by the formation of the desired allene intermediate.…”