Bicyclo hept-2-enes synthesis

Hybridalactone, a novel marine derived eicosanoid from Laurencia hybrida, appears to be biosynthesized by a unique pathway from eicosapentaenoic acid. The synthesis of hybridalactone was carried out enantiospecifically from (+)-bicyclo[3.2.0]hept-4-ene-l-one so as to provide proof of stereochemistry (Ref. 4). 

Annual Volume 71 contains 30 checked and edited experimental procedures that illustrate important new synthetic methods or describe the preparation of particularly useful chemicals. This compilation begins with procedures exemplifying three important methods for preparing enantiomerically pure substances by asymmetric catalysis. The preparation of (R)-(-)-METHYL 3-HYDROXYBUTANOATE details the convenient preparation of a BINAP-ruthenium catalyst that is broadly useful for the asymmetric reduction of p-ketoesters. Catalysis of the carbonyl ene reaction by a chiral Lewis acid, in this case a binapthol-derived titanium catalyst, is illustrated in the preparation of METHYL (2R)-2-HYDROXY-4-PHENYL-4-PENTENOATE. The enantiomerically pure diamines, (1 R,2R)-(+)- AND (1S,2S)-(-)-1,2-DIPHENYL-1,2-ETHYLENEDIAMINE, are useful for a variety of asymmetric transformations hydrogenations, Michael additions, osmylations, epoxidations, allylations, aldol condensations and Diels-Alder reactions. Promotion of the Diels-Alder reaction with a diaminoalane derived from the (S,S)-diamine is demonstrated in the synthesis of (1S,endo)-3-(BICYCLO[2.2.1]HEPT-5-EN-2-YLCARBONYL)-2-OXAZOLIDINONE. 

Starting from optically active 1-chlorovinyl p-tolyl sulfoxide derived from 2-cyclohex-enone, the asymmetric synthesis of cyclopropane derivative (85) was realized (equation 23) . Addition reaction of lithium enolate of tert-butyl acetate to 83 gave the adduct (84) in 96% yield with over 99% ee. Treatment of the latter with i-PrMgCl in a similar way as described above afforded optically pure (15,6/ )-bicyclo[4.1.0]hept-2-ene (85) in 90% yield. 

A practical synthesis of bicyclo[2.1.0]pentane (6) by thermolysis of 2,3-diazabicyclo[2.2.1]-hept-2-ene has been reported in detail.13 It has already been shown that the conversion of 2,3-diazabicyclo[2.2.1]hept-2-ene to bicyclo[2.1.0]pentane involves a diradical intermediate.14... 

This method of nitrogen elimination from tetrahydropyridazines is frequently used in the synthesis of polycyclic systems. The thermolysis, as well as photolysis, of 2,3-diazabicy-clo[2.2.1]hept-2-enes gave bicyclo[2.1.0]pentanes via intermediate formation of cyclopenta-1.3-diyl, from which bicyclic compounds with one three-membered and one four-membered segment are formed this type of reaction is discussed in Houben-Weyl, Vol. E17b, pp 1089-1108 and 1163-1166. 

Table 4 Synthesis of 6-thia-2,4-diaza-bicyclo[3.2.0]hept-1 (5)-ene-3-thione 82...

In a similar heterocyclic quinodimethane ring construction strategy, the hexacyclic adducts (64) were isolated in good yield upon condensation of appropriately functionalized indole imines with ( )-bicyclo[2.2.1]hept-5-ene-2-carboxylic acid chloride (Equation (35)) (88JA2242). In a demonstration of the utility of this new method for indole alkaloid synthesis, further transformations conducted on compound (64 R = R2 = H, R3 = Et) were shown to lead to ( —)-16-methoxy-tabersonine. 

Although small in number, the investigations summarized above show that the Cope rearrangement of 7-(l-alkenyl)bicyclo[4.1.0]hept-2-enes is an effective method for the synthesis of usefully functionalized bicyclo[3.2.2]nona-2,6-dienes. 

The double elimination of 1,1-dichlorocyclopropanes with potassium tert-butoxide to give cycloproparenes is an important variant of the reaction discussed in Section 5.2.2.1.2.3. When a six-membered ring fused to the cyclopropane contains a double bond, the elimination is accompanied by isomerization of the new double bonds to give an aromatic ring (Table 7). The reaction is illustrated by the synthesis of bicyclo[4.1.0]hepta-l,3,5-triene (l//-cyclo-propabenzene, 3) in two steps from cyclohexa-1,4-diene (1), the first step being dichlorocarbene addition to the diene to give 7,7-dichlorobicyclo[4.1.0]hept-3-ene... 

Synthesis from xylose The xylose derivative 47, obtained from 5,5-bis-benzyloxy-7-oxa-bicyclo[2.2.1]hept-2-ene (45), has been used in the synthesis of (-P)-castanospermine (1) (Scheme 6). Bromination of 45 occurred exclusively on the less hindered convex face of 45, followed by stereoselective migration of the endo OBn group of the acetal to give 46, which subsequently converted to 47. Mesylation of 47 followed by cyclization with ammoifia gave 48, whose protection, hydrolysis, acetylation and cyclization by an intramolecular Wittig-Homer condensation gave 49. Conversion of 49 into epoxide 50... 

Annulation of heterocycles with a cyclobutene ring has been achieved by photochemical (2 + 2)-cycloaddition with acetylenes. Both maleic anhydride and N-substituted maleimides yielded 3-oxa- or 3-aza-bicyclo[3.2.0l-hept-6-ene-2,4-diones (167).,89,9° Vinylene carbonates also entered into a cycloaddition reaction with acetylenes to afford 168, which has been employed as starting material for the synthesis of cyclo-butadiene(tricarbonyl)iron or cyclobutenedione.19,-193 3,4-Dihydro-2/f-pyran and 5-methyl-2,3-dihydrofuran reacted with diphenylacetylene to... 

This paper describes the synthesis, characterization and application of poly(7-oxa bicyclo[2.2.1]hept-5-ene-2,3-diacetate) (PI )a precursor for polyffurylene vinylene). 

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