UV-mediated decomposition of diazomalonates in benzene: Unexpected access to functionalized bicyclo[3.2.0]heptane skeleton

Upon irradiation with 300-nm UV light, the photolysis of diazomalonates in benzene unexpectedly affords 2,6-dicarboxylate bicyclo[3.2.0]hepta-2,6-dienes in low yields. These products are proven to be derived from cyclohepta-1,3,5-triene intermediates presumably via a tandem 1,5-carboxylate migration/[2+2] cycloaddition sequence.     

First synthesis of 2,6-diazabicyclo[3.2.0]heptane derivatives

The first synthesis of 6-phenyl-2,6-diazabicyclo[3.2.0]heptane 1 and its orthogonally protected precursor 2 is herein reported. Our strategy enables to chemically address the two nitrogen atoms of 2,6-diazabicyclo[3.2.0]heptane core individually and selectively, thus allowing rapid access to several subsets of widely substituted fused azetidines.     

Gasphasen-Thermolyse Methyl-substituierter Bicyclo[3.2.0]hept-2-en-7-one

Gas phase thermolysis of methyl-bicyclo [3.2.0] hept-2-en-7-ones. Irradiation of methylnorbornenones 5a , 5b , 5c and 5e leads to the methyl-bicyclo-[3.2.0]hept-2-en-7-ones 4a , 4b , 4c and 4e , respectively. Upon flash thermolysis of these βγ-unsaturated ketones dihydrotolualdehydes 9 and 10 and tolualdehydes 11 are formed as major products. The formation of these aldehydes is rationalized as involving methyl substituted ketenes 6 and conjugated heptatrienaldehydes 7 as intermediates. From the position of the methyl group in the stable pyrolysis products 9 , 10 and 11 the occurrence of a thermally induced [1, 5]-sigmatropic shift of the formyl group in 1,2-dihydro-tolualdehyde 8 is inferred.     

A non-photochemical approach to the bicyclo[3.2.0]heptane core of bielschowskysin

An asymmetric synthesis of the tricyclic core (-)-1 of the marine diterpene bielschowskysin is described. In particular, a methodology was developed to introduce the crucial quaternary center at C-12.     

Synthesis of purine nucleosides built on a 3-oxabicyclo[3.2.0]heptane scaffold

The photochemical [2 + 2] cycloaddition of chiral 3-chloro and 3-fluoro-5-hydroxymethyl-2(5H)-furanone to ethylene and acetylene has been studied. The effect of the halogen atom on the chemical yield and facial diastereoselectivity of the cycloaddition process has been evaluated. From the major anti cycloadducts, practical syntheses of several purine cyclobutane and cyclobutene-fused nucleosides containing a halogen atom have been developed. The anti-HIV activity of the new nucleoside analogues has been evaluated.     

Theoretical Study of the Photochemical Reaction Mechanism of Bicyclo [4.1.0 ] heptane

IntroductionPhotochemical reactions, which involve a three-membered ring, have been of great interest to experi-mental photochemists[1—10]. A main reason for thisphenomenon is that the cyclopropane ring exhibits somereaction characteristics of double bon…     

Polycyclic azetidines. I. The preparation of benzo [c]-cis-6-azabicyclo[3.2.0] heptane

The title compound was prepared from compounds readily obtained from 2-carbomethoxy-I-indanone oxime ( 5 ) or from the N-chlorosulfonyl isocyanate adduct of indene ( 9 ). Apart from its ability to undergo transformation to the azetidine, compound 9 upon refluxing with excess LAII was found to undergo reductive decompostion to cis-2-hydroxymethyl-1-indanamine ( 2 ).     

Umwandlung von Bicyclo [3.2.0]hept-2-en-6-on in Cyclopentadienessigsäure-Derivate

Conversion of Bicyclo [3.2.0]hept-2-en-6-one into Cyclopentadienylacetic Acid Derivatives The reaction of a mixture of 4exo-bromobicyclo [3.2.0]hept-2-en-6-one ( 2 ) and -7-one ( 3 ) with O- or N-nucleophiles yielded cyclopentadien-5′-yl-acetates 4a–f or-acetamides 4g–h . Due to their rapid isomerization, the products 4 were not isolated, but some of them were demonstrated spectroscopically or captured in situ with maleimide as 10′-substituted norbornene derivatives 7 . The formation of 4 from 2/3 involves a fragmentation of the bond between the carbonyl and the bridge-head C-atom, induced by the attacking nucleophile and the leaving Br-ion and aided by the relief of the four-membered ring strain. Some of the isomerization products of 4 , i.e. the cyclopentadiene-1′-yl- and 2′-yl-acetyl derivatives were captured with maleimide as the 1′- and 8′-substituted norbornene-derivatives 8 and 9 . Two C-nucleophiles did not induce the fragmentation: sodium acetylacetonate substituted the Br-atom and sodium (diethoxyphosphoryl)ethoxycarbonylmethide condensed with the carbonyl group of 2/3 , yielding 11/12 and 13/14 , respectively.     

Bicyclo [2.2.1]heptane as cyclopentane precursor. synthesis of benzhydropentalenes enroute to terpenoids

The synthesis of a bicyclo[2.2.l] heptane derivative and its transformation to two different cyclopentanoid derivatives and through intramolecular functionalisation is described for entry into diterpene and sesquiterpene.     

Bicyclo[2.2.1]heptane derivatives containing two vicinal CFC1 groups. The tendency tocis-dehalogenation

Dehalogenation ofexo-cis-2,3-dichloro-2,3-difIuoro-1,2,3,4,4a,-5,8,8a-octahydro-l,4,5,8-dimethanonaphtalene yields 2,3-difluoro-l,4,4a,5,8,8a-hexahydro-1,4,5,8-dimethanonaphthalene as the sole product, whereas the isomerictrans-dichloride affords a mixture of the above product with 2-chloro-3-fluoro-l,4,4a,5,8,8a-hexahydro-l,4,5,8-dimethanonaphthalene (2 1 respectively).Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 411–413, February, 1993.     

Synthetic studies of pestalotiopsin A: asymmetric synthesis of the 2-oxabicyclo[3.2.0]heptane substructure

A functionalized 2-oxabicyclo[3.2.0]heptan-3-one derivative, possessing all the skeletal carbons of pestalotiopsin A, has been synthesized. For the preparation of intermediary cyclobutane derivatives in enantioenriched form, the Lewis acid-catalyzed [2+2] cycloaddition of N-propiolated Oppolzer’s camphorsultam with dimethylketene bis(trimethylsilyl) acetal followed by a stereoselective 1,4-hydride addition/protonation, has been developed.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

Conformational analysis of 7,7-dichloro-2,5-dioxabicyclo[4.1.0] heptane by NMR

The ¹H NMR spectra of 7,7-dichloro-2,5-dioxabicyclo-[4.1.0]heptane ( 1 ) were analyzed through the application of programs NMRIT and NMREN2.

1 See Ref. 1.

The half-chair conformation of 1 was obtained from the vicinal coupling constants by the Buys R method.

2 See Ref. 2.