The Preparation of Optically Pure 7‐Oxabicyclo [2.2.1]hept‐2‐ene Derivatives. The CD Spectrum of (+)‐(1R)‐7‐Oxabicyclo [2.2.1]hept‐5‐en‐2‐one

Abstract

Summary(-)-1-Camphanoyloxyacrylonitrile (= (-)-1 -cyanovinyl camphanate; 1) obtained from the commercially available ( -)-camphanoyl chloride and 2-0x0-propiononitrile added to furan at 20" in the presence of CU(BF,)~. 6 H 2 0 or Zn12 and gave a mixture of 2-cyano-7-oxabicyclo [2.2. IIhept-5-en-2-yl camphanates (2-5) from which isomer 5 could be obtained pure by crystallization. The latter was transformed into (+ )-( 1 R)-7-oxabicyclo [2.2.1]hept-5-en-2-one (6) in high yield and optical purity. Adducts 2-4 were recycled into 1 + furan by heating in toluene, and (-)-camphanic acid was recovered after saponification of 5. The absolute configuration of 6 was deduced from its CD spectrum which showed two 1200-cm-' Franck-Condon series for its n + nEo transition.Introduction. - [5], and other products of biological interest [6]. This bicyclic framework is available through the Diels-A Zder addition of furans to strongly activated dienophiles (71, and these often sluggish cycloadditions can be accelerated by applying very high pressure [8] or, more simply, by adding catalytic amounts of Cu (1)Optically pure 7-oxabicyclo [2.2.l]hept-5-en-2-~1 derivatives should have a particularly promising future in the synthesis of natural products and compounds of biological interest such as nucleosides [ 1 11 and cyclitols [ lOa], because the stereoand regioselectivity of electrophilic additions to their C, C double bond can be directed by modifying the nature of the substituents at C (2) [ 121'). We report now

5a-Carba-β-D-, 5a-Carba-β-L- and 5-Thio-β-L-xylopyranosides as New Orally Active Venous Antithrombotic Agents

“…± Since the ethereal link between the conduritol-B moiety and the aglycone (4-ethyl-7-hydroxy-2H-1-benzopyran-2-one) will be generated through a S N 2 displacement, a suitably semi-protected conduritol-F intermediate was required. Among the numerous synthesis of conduritol-F that have been proposed [10], the one by Le Drian [11] has demonstrated that racemic (AE)-12 can be derived from the Diels-Alder adduct (AE)-7 of furan to 1-cyanovinyl acetate via (AE)-8 ± 11, whereas enantiomerically pure ()-12 and (À)-12 can be derived with the same ease from the Diels-Alder adducts of furan to enantiomerically pure 1-cyanovinyl esters [12]. The synthesis of (AE)-12 [11] involves the base-induced isomerization of the 7-oxabicyclo[2.2.1]heptan-2-one derivative (AE)-10 into cyclohex-2-enone (AE)-11 (91%).…”

Masked Ketenes as Dienophiles in the Diels–Alder Reaction

“…[32] Modifications of the acetate functionality are also known: in 1997, MaGee reported the incorporation of a more electron-withdrawing 2,4-dinitrobenzoate moiety (dienophile 11), providing an increase in DA reactivity of ,5-6 times (comparable reactivity with acrylonitrile (35), discussed in the section Acrylonitriles). [33] In addition, Vogel and coworkers demonstrated that by the incorporation of chiral auxiliaries, [34][35][36][37][38][39] such as in tartaric acid-derived dienophile 12, [34] enantiomerically pure ketones were accessible via this methodology.…”

Optical resolution of 7‐oxabicyclo[2.2.1]hept‐21‐ene derivatives. Diastereoselectivity in the formation of cyanohydrine‐brucine complexes

“…Particularly useful is the ability to isolate the endo -carbonitrile 4 in its optically pure form. This is the minor isomer obtained from the Diels-Alder additions of furan to a-acetoxyacrylonitrile and (-)-1-cyanovinyl camphanate [4].…”

“…[9] is also reported. The 2x11,-catalyzed Diels-Alder addition [4] of furan to or-acetoxyacrylonitrile ( = 1-cyanovinyl acetate) gave a 4: 1 mixture (90 % crude) of the cxo-us. endo -carbonitriles (5)-3 and (&)-4 [9].…”

“…Some derivatives have also been shown to exhibit antitumor [2] or antiinflammatory activity [3]. We recently reported the preparation of two optically pure 7-oxabicyclo[2.2. llheptane derivatives, (+)-1 and (+)-2 [4]. Systems such as these can be viewed as 'naked sugars' since positions C(3), C (5), and C(6) can be stereospecifically functionalized with a variety of substituents; electrophilic additions to the C(5), C(6) double bond are highly stereoselective (51 [6], and electrophilic substitution of a H-atom at C (3) in 1 (and other related ketones) can also be highly stereoselective under either thermodynamic or kinetic control [7].…”