Concise Synthesis of Novel Oxa-Bridged Compounds

Abstract

[structures: see text] A stereoselective strategy for the replacement of the 1,2-dihaloalkene bridge of tetrahalonorbornyl derivatives by an oxygen bridge involving stepwise controlled oxidation, cleavage of the dione thus formed, and reiterative intramolecular S(N)2 displacement of two bridgehead halogens is devised. The synthesis of four highly strained pentacyclic bis-oxa-bridged derivatives 10, 27, 28, and 29 with interesting structural variations is presented. The two oxa bridges are syn to each other, separated by central cyclohexane and cycloheptane rings in 10 and 27, while they are anti to each other and are separated by central cyclopentane and furan rings in 28 and 29. In the case of the highly symmetric bis-oxa-bridged derivative 10 the two syn oxa bridges constrain the central cyclohexane ring into the boat form. The endo,anti,endo 2:1 bis adducts of 1,2,3,4-tetrahalo-5,5-dimethoxycyclopenta-1,3-diene with cyclopentadiene were prepared for the first time, while the reactivites of previously unexplored bis adducts derived from furan and cycloheptatriene were revealed.

Preparation, structures and preliminary host–guest studies of fluorinated syn-bis-quinoxaline molecular tweezers

“…A Diels–Alder reaction of cyclohexadiene ( 5 ) with ketal 7a furnished exclusively the syn -bis-adduct 8a [20] which was then converted to the canary-yellow tetraketone 10 by Khan’s original RuCl 3 -catalyzed oxidation protocol [21–23] since Chou’s “optimized” procedure was somewhat capricious in our hands. The twofold condensation with di- or tetrafluoro- o -phenylenediamine ( 12b , c ) [24–25] provided access to the novel fluorinated species 15b – c in acceptable yields (60–70%).…”

“…The X-ray structure determination of target compound 16c confirmed indirectly the correct assignment of isomers 9b and 9b′ (vide infra). Oxidation of 9b with Khan’s original protocol [21–23] and condensation of the resulting tetraketone 11 with o -phenylenediamine 12a or the fluorinated derivatives 12b – c resulted in the new non-fluorinated parent compound 16a and the three fluorinated scaffolds 16b – c , respectively. All new syn -bis-quinoxalines were purified by flash-chromatography on silica gel and obtained as off-white powders in 60–75% yield after recrystallization from methanol.…”

BF3-Et2O mediated skeletal rearrangements of norbornyl appended cyclopentanediols

“…R f (10% ethyl acetate in hexane) 0.6, viscous liquid, yield 87% (1.36 g, 3.79 mmol); 1 H NMR (400 MHz, CDCl 3 ) δ 3.57 (s, 3H), 3.53 (s, 3H), 3.24 (s, 1H), 3.19 (d, 1H, J = 7.8 Hz), 3.02-2.97 (m, 1H), 2.04 (dd, 1H, J = 9.0, 15.4 Hz), 1.70 (dd, 1H, J = 3.2, 15.4 Hz), 1.36 (s, 3H); 13 C NMR (100 MHz, CDCl 3 ) δ 130. 3, 129.8, 113.7, 77.7, 77.2, 75.5, 68.7, 63.7, 56.3, 52.3, 51.6, 31.6, 17.8;IR (KBr) 2950, 2812, 1604, 1441, 1185 (1aR,1bS,2S,5S,5aS,6aS)-2,3,4,5-Tetrabromo-7,7-dimethoxy-6a-methyl-1b,2,5,5a,6,6a-hexahydro-1aH-2,5-methanoindeno [1,2-b]oxirene (10 6, 114.3, 71.2, 70.0, 69.0, 63.9, 57.8, 53.9, 52.8, 51.6, 31.7, 17.8 (2S,3aS,4S,7S,7aS)-4,5,6,7-Tetrachloro-8,8-dimethoxy-2-methyl-2,3,3a,4,7,7a-hexahydro-1H-4,7-methanoinden-1-one (11). To a stirred solution of compound 7 (50 mg, 0.14 mmol) in toluene (1.8 mL), was added BF 3 -Et 2 O (0.42 mmol) at room temperature.…”

Synthesis and thermal properties of rigid oxa-bridged-containing dimers and tetramers

“…9b Recently, we have demonstrated an easy access to sterically constrained oxa-bridged derivatives. 14 We thought of utilizing oxabridged derivatives as the rigid central spacers to construct novel type of liquid-crystalline dimeric compounds and rationalize and analyze accordingly their thermal behaviours and optical properties. Our strategy consisted of incorporating the oxa-bridged derivatives 8, 9 and 10 ( Fig.…”

“…15 A similar approach for the preparation of bis-oxa-bridged tetrol 10, starting from the corresponding tetramethyl ester 11, 14 furnished an isomeric mixture. 14 The tetrol 10 was finally obtained by treating 11 with DIBAL-H in dichloromethane (Scheme 1).…”