cis,trans ‐Oxaaza‐bis‐σ‐homobenzole – 4 H ‐1,4‐Oxazocine

Abstract

cis,truns-Oxaaza-bis-o-homobenzenes -4H-1,4-OxazocinesThe cis-oxaaza-bis-0-homobenzene framework has been synthesised via two routes starting from readily accessible materials (11, 25). As expected the N-SO,R derivatives 3a, b are sufficiently stable to be isolated; on heating, they readily and quantitatively undergo [,2 + . 2 + ,,2]-cycloreversion to the 4H-1,4-oxazocines 6a, b (3b: t1,2 (60°C) = 33.2 min; AG* = 104.0 kJ.mol-I). The latter prefer a non-planar, folded conformation. Using a precursor of 3 b (27a), the thermally stable trans-oxaaza-bis-o-homobenzene 9 was obtained in very small yield (2 -6 % ) by two alternative pathways.In den cis-konfigurierten Bis-o-homobenzol-Gerusten A sind die stereoelektronischen Voraussetzungen fur die [,2 + ,,2 + a2]-Cycloreversion uber den bishomobenzoiden Ubergangszustand B derart gunstig, daD bei breiter Variation der Brucke X sowohl in der [1

Synthesis of the first examples of 1,4-benzodioxocines

“…These spectral properties are similar to those of the non-aromatic monocyclic 174-dioxocines3 and 1,6-benzodioxocines7 and are different from those of the monocyclic 1,4-diazocinesS and 1 ,4-oxazocines,6~9 which are known to have a planar structure and aromatic character. The above data lead to the conclusion that the 1,4-benzodioxocines (6) possess no substantial diamagnetic ring current due to the lower tendency of the oxygen atom to x-electron delocalization and are thus non-aromatic.…”

“…signals (6 5.46-6.34) of the heterocyclic ring protons in (6) lie in the olefinic range and the vicinal coupling constants (J2,3 3.4 and J5,6 7.8 Hz) are relatively small. Moreover, compounds (6) exhibit 13C resonances at relatively low field strength for all the eight-membered ring carbon atoms. These spectral properties are similar to those of the non-aromatic monocyclic 174-dioxocines3 and 1,6-benzodioxocines7 and are different from those of the monocyclic 1,4-diazocinesS and 1 ,4-oxazocines,6~9 which are known to have a planar structure and aromatic character.…”

“…the 1,4-benzodiheterocines, have not been reported. Here we report the synthesis of the first examples of 1,4-benzodioxocines (6) by a new route for heterocines.…”

Highly Functionalized Cyclohexenyl Systems: Enzymatic Resolution and Selective Oxirane Opening Reactions of p-Benzoquinone Derivatives

“…Other Lewis acids including LiClO 4 9c and BF 3 ·OEt 2 provided useful yields in some cases but did not prove to be general over a range of nucleophiles. The combination of zinc sulfate and sodium azide produced azido alcohol 6f in high yields . While oxirane openings with carboxylic acids are rare in the literature, the new procedure developed by Jacobsen et al. 13a,b incorporating a (salen)Co(II) complex (prepared from Co(OAc) 2 and ( S , S )−(+) N,N -bis(3,5-di- tert -butylsalicylidene)-1,2-cyclohexanediamine) 13c efficiently facilitates oxirane opening of 5 with acetic acid to provide the differentially protected triol derivative 6i in high yield.…”

In Pursuit ofcis,cis,cis‐Cyclonona‐2,5,8‐triene‐1,4,7‐trione – An Adventure in Medium‐Sized Ring Chemistry

“…[45] The experimental work launched high-level calculations [46] that confirmed early estimates [33,47] as to the "aromaticity" of the [σ2s + σ2s + σ2s]-trishomobenzenoid transition states B and related the much higher kinetic stabilities of the triscyclobuta analogues to the "antiaromaticity" of the corresponding transition states. A very rewarding extension of our synthetic activities centered on cis-(bis)hetero-bis-σ-homobenzenes (X,Y = NR,NR; [48] O,NR; [49] CHR,NR [50] ) and the derived 1,4-(hydro)diheterocines and hydroheterocine anions, another novel class of medium-ring heterocycles. [45] Conflicting theoretical predictions [51] as to the latter's potential "aromaticity" were clarified when N-electron donor/acceptor substitution allowed the isolation of nonplanar, "localized" as well as of planar, "delocalized" rings.…”