Yoshinobu Odaira

Synthesis, Structure and Reactivities of [6]Paracyclophanes.

Abstract The synthesis, structure and reactivities of [6]paracycophanes 2a-c, the smallest bridged [n]paracydophanes so far isolated, are described. The parent hydrocarbon 2a has been efficiently synthesized by oxidative decarboxylation of [6.2-2]propellenecarboxylic acid (7) by lead tetraacetate. The 8-carbomethoxy derivative 2b has been quantitatively synthesized by thermal valence isomerization of the [6.2.2]propelladiene (4b) (Dewar isomer of 2b). X-Ray structure analysis of the crystalline 2c has revealed that the benzene ring of 2c severely deformed into a boat conformation with deformation angles of α= 20.5° and β = 18.5°. Furthermore, the bond angles of the bridging chain (C(2), C(3), C(4) and C(5)) are considerably expanded from the normal sp3 angle. Vaporphase thermolysis of 2a gives the spiro triene 12 via homolysis at the benzyl position. Add-catalyzed isomerization of 2a with trifluoroacetic add takes place readily to afford the meta and ortho isomers 13a and 14a in a ratio of 1:3. UV irradiation of the ester 2b brings about valence isomerization to the Dewar isomer 4b which isomerizes slowly to the prismane derivative 15a on further irradiation. A [4+2] cycloaddition of 2a with N-phenyl-l,2,4-triazoline-3,5-dione occurs at room temperature to give mainly adduct 16. Addition of bromine to 2a takes place to furnish quantitatively the unstable 1,4-addition product 18. Oxidation of 2a with mCPBA readily takes place to give the dienone dimer 20 which affords on UV irradiation the cage diketone 21 derived from intramolecular photocycloaddition.

Stereocontrolled total synthesis of (±)-isocomene and (±)-β-isocomene via ring enlargement

A total synthesis of (±)-isocomene(1) and (±)-β-isocomene (2) employing a chelation-controlled regioselective epoxide–carbonyl rearrangement as the key step has been realized.

A new strategy for construction of angularly fused tricyclic ring systems. Transannular bond formation of bicyclic enones via photochemical intramolecular hydrogen abstraction

Abstract Tricyclic ketones 3a, b and 7a–c having angularly fused 5-6-5 or 5-7-5 ring system have been efficiently prepared by irradiation of bicyclic enones 1 and 2.

Chelation-controlled regioselective epoxide–carbonyl rearrangement: a ring enlargement route to (±)-modhephene

A new formal total synthesis of (±)-modhephene (1) employing a chelation-controlled regioselective epoxide-carbonyl rearrangement as the key step is described.

Complexation between novel cyclophane host and polar guests by hydrogen bonding

Abstract A novel cyclophane host, 2, 11, 20-trihydroxy-2,5,8,11,14,17,20,23,26-nonamethyl [3.3.3]paracyclophane ( 4 ), has been synthesized and found to form complexes with polar organic guest molecules by hydrogen bonding.

A novel synthesis of (±)-descarboxyquadrone

Abstract The novel synthesis of descarboxyquadrone (3) and its model compound (4) by using the acid-catalyzed rearrangement of [4.3.2]propellanones is described.

Cyclobutyl-cyclopropylcarbinyl type rearrangement of 1-oxaspirohexane derivatives. A new entry to functionalized norcaranes

Abstract The acid-catalyzed rearrangement of the 1-oxaspirohexane derivatives 2a,b,d gave the corresponding functionalized norcaranes 3a,b,d in moderate to good yields.

Synthesis of bicyclo[6.2.2] bridgehead dienes

Bicyclo[6.2.2]dodecadienes (2), (3a), and (3b) having two bridgehead double bonds were synthesized by the pyrolysis of the acetate (1).

Photochemical reactions of aromatic esters—I : Photochemical synthesis of new oxetanes from aromatic esters with 1,1-diphenylethylene

Abstract Irradiation of dimethyl terephthalate IIIa with 1,1-diphenylethylene IV afforded an oxetane Va as a sole adduct. The structure of the oxetane was established on the basis of its spectroscopic properties. Similar irradiation of p - or o -cyanobenzoate with IV gave a corresponding oxetane Vb or Vc, respectively. Trimethyl trimesate VII could also add to IV photochemically to form an oxetane VIII. On the other hand, irradiation of dimethyl phthalate IIId with IV could not give an oxetane Vd but an olefin VI which was considered to be produced through the elimination of a formaldehyde molecule from an unstable intermediate oxetane Vd. A reactive species of the photocycloaddition was suggested to be an n -π * triplet state of the aromatic ester from the evidences of the phosphorescence emissions of the esters and the direction of the addition.

Novel photocycloaddition of 2-naphthols to ethylene in the presence of Lewis acid

Abstract The photoreaction of 2-naphthols 1a-e with ethylene in the presence of aluminum halide gave the [2+2] cycloadducts 3a-e in good yields.