Reactions of phthalans with dienophiles. III. Formation of homoquinones by reaction of 1,1-diethoxyphthalans with quinones

Abstract

Treatment of 1,1-diethoxyphthalan with 1,4-benzoquinone gave the homoquinone, ethyl 2-[(1′R*,6′S*,7′S*)-2′,5′-dioxo-3′-norcaren-7′-yl]benzoate, 3, instead of an anthracene derivative expected of a normal cycloaddition reaction. The structure of the homoquinone was deduced from an examination of its spectroscopic properties (ir, 1H nmr, and 13C nmr) and verified by an X-ray crystallographic study. The homoquinone, 3, is triclinic, P1, with a = 10.601(2), b = 10.434(3), c = 6.491(3) Å, α = 105.53(3), β = 95.21(2), γ = 100.66(2)° and has two formula units per unit cell. The crystal structure was determined by direct methods and refined to R1 = 0.059, R2 = 0.048, based on 2378 independent reflections. The data set was obtained using a Syntex P21 diffractometer and MoKα radiation. Bond angles and distances within the molecule are normal. Homoquinones were also isolated as major products of reaction of 1,1-diethoxyphthalan and 5,6-dimethoxy-1,1-diethoxyphthalan with 1,4-benzoquinone and 1,4-naphthoquinone. A mechanism for the formation of homoquinones is offered that involves the same type of transient intermediates proposed for the reactions of 1,1-diethoxyphthalans with activated acetylenes and ethylenes.

Bis{1a,8b-dihydro(1,1-2H2)-2H-benzo[a]cyclopropa[c]cyclohepten-2-one}hydrogen(I) hexachloroantimonate, [H(C12H8D2O)2][SbCl6]

“…The other two sides of the cyclopropane group differ significantly [by 3.30-where 0-= (o'12+ 0"22) I/2] with the C(1)-C(8) bond which is nearer the ketone being longer. While the errors preclude certainty, a similar effect has been suggested in three systems previously studied (Dusausoy et al, 1981) where the C-C bond nearer the ketone consistently has a higher mean length [range 1.499 (11) Contreras et aL, 1981). This is presumably caused by the very stong hydrogen bond between the carbonyl groups.…”

“…Thus the short C(3)-C(4) bond [1.341 (8)A] suggests that the double bond has not been extensively delocalized. Further the C-C distances in the cyclopropane group have not changed significantly from other similar neutral molecules (Dusausoy, Hanquet & Guilard, 1981;Contreras, MacLean, Faggiani & Lock, 1981). In particular there is no significant lengthening of the C(1)-C(7) bond [1.544 (8)A vs range 1.513 (11)-1.555 (7), ave. 1.535(10)A1 such as was observed for the 2-hydroxyhomotropyllium ion [1.626 (8)A] (Childs et al, 1982).…”

X-ray Structures of Cyclophanes Derived from Naphtho[1,2-c:5,6-c]difuran and the Synthesis, Structure, and Reaction Kinetics of Its 1,3,6,8-Tetrasilylated Derivative

“…There are several problems associated with the high reactivity of IBF and its reactive benzologues. The parent compound is stable only in solution at room temperature. , It is unstable in the presence of acid and must be trapped in situ when generated under conditions of acid catalysis. , This makes stoichiometric control of reactions difficult, a problem that is compounded in Diels−Alder reactions in which the dienophile is also highly reactive. In our work preparing cyclophanes, high reactivity results in substantial competing polymerization.…”

“…This solution was stirred for 10 min before the addition of tert-butyldimethylsilyl chloride (0.63 g, 4.2 mmol). The mixture was warmed to (21), 607 (15), 147 (15), 91 (15), 73 (70), 57 (22), 55 (100). Anal.…”

Stereoselective Cyclopropanation to Homoquinones from Phenacyl Carbenes Obtained through Quinone-Electrogenerated Bases

“…Homoquinones ( 3 ) were characterized by its IR, MS, 1 H NMR, 13 C NMR, NOE-2D and correlation COSY spectroscopic properties. Also by comparison with other, already described, homoquinone frames …”