Intramolecular photocycloaddition reactions of 4-phenoxybut-1-enes

4-Phenoxybut-1-ene undergoes both ortho and meta intramolecular photocycloaddition on 254 nm irradiation: in the latter process the addition is directed by the alkoxy tether to the arene 2,6-positions. Methyl substitution on the ethene and arene units does not affect the regiochemistry of the reaction but the presence of a 2′-methoxy group inhibits the meta process and only the ortho addition occurs.     

Intramolecular deuterium isotope effects in the meta photocycloaddition of aromatic compounds to alkenes

The effect of substitution of hydrogen by deuterium in some aromatic compounds on product distributions in the meta photocyloaddition to alkenes was investigated. The isotope effects found are in agreement with a polar mechanism.     

Intramolecular photocycloaddition reactions of 4-alkenyloxycoumarins

Intramolecular [_π2 + _π2] photocycloaddition reactions are reported for 4-(but-3′-enyloxy) and 4-(pent-4′-enyloxy) coumarins.     

New molecular entities via intermolecular meta photocycloaddition

The intermolecular meta photocycloaddition of 1,3‐dihydroisobenzofuran and 1,3‐dihydroisoindole‐2‐carboxylic acid methyl ester with cyclopentene and 2,5‐dihydrofuran affords two new classes of photoadducts. The photoadducts were identified by the SORT&gen algorithm as New Molecular Entities in two‐dimensional scaffold space. The structures of the adducts were established by NMR spectroscopy and the stereo‐, regio‐ and chemoselectivity of the reactions is discussed.     

Intramolecular photocycloaddition of β-stilbazoles tethered by silyl chains

Intramolecular (2+2) photocycloaddition of β-stilbazoles tethered by silyl chains took place with high efficiency. Complexation with dicarboxylic acid or catechol further enhanced both the efficiency and stereoselectivity.     

Asymmetric induction in intramolecular meta photocycloaddition: cyclodextrin-mediated solid-phase photochemistry of various phenoxyalkenes

[reaction: see text]. An approach to the asymmetric intramolecular meta photocycloaddition of phenoxyalkenes is described. The beta-cyclodextrin complexes of several phenoxyalkenes have been synthesized and irradiated in the solid phase. The effect of the CD-hosting on the regio- and enantioselectivity is discussed. Values of ee up to 17% were obtained.     

Intramolecular photocycloaddition of cyclic thioimides as a method for heterocyclic synthesis

Cyclic thioimides undergo photocycloaddition with tethered pi-bonds in a regiospecific manner to afford spirocyclic amidothietanes. These highly strained multicycles undergo a subsequent ring opening reaction to furnish novel fused pyrrolizinones.     

Intramolecular [2+2] photocycloaddition of substituted isoquinolones: enantioselectivity and kinetic resolution induced by a chiral template

From simple to complex: Starting from easily accessible isoquinolones 1 (X=Br, OH), complex cyclobutane photoproducts such as compound 2 can be obtained with high enantioselectivity (88-96?%?ee) through the use of a chiral template. Compound 3, which was isolated in 53?%?ee starting from a racemic substrate, is the product of a unique, unprecedented kinetic resolution process.     

Intramolecular pyridone/enyne photocycloaddition: partitioning of the [4 + 4] and [2 + 2] pathways

Intramolecular photocycloaddition (>290 nm) between a 1,3-enyne and a 2-pyridone is far more selective than the intermolecular version; a three-atom linkage both controls regiochemistry and separates the [2 + 2] and [4 + 4] pathways. All four head-to-head, head-to-tail, tail-to-head, and tail-to-tail tetherings have been investigated. Linkage via the ene of the enyne leads to [2 + 2] products regardless of alkene geometry, whereas linkage through the yne results in [4 + 4] cycloadducts. The bridged 1,2,5-cyclooctatriene products of [4 + 4] cycloaddition are unstable and undergo a subsequent [2 + 2] dimerization reaction.     

Intramolecular photocycloaddition of dioxenones with alkynes: formation of secondary photoproducts from cyclobutene photoadducts

[Reaction: see text] Intramolecular photocycloaddition of 4 leads to the formation of cyclobutene photoadduct 5. Secondary photoreaction of 5 then affords either cyclobutane 19 or the bridged product 7, as a function of R (H or TMS).     

[6+6]-benzo/benzo - photocycloaddition reactions

Cyclobutane-formation between “face-to-race” oriented benzenoid chromophoric units has been observed in 1,6-diene- (B) (1b–d/4a–d), not, however, in 1,5-diene-derived (C) (7a–c) skeletons.     

Intramolecular sulphonamidomethylation. Part II. Fused heterocycles from 2-phenylethanesulphonamides

1,2,4,5-Tetrahydro-3,2-benzothiazepine 3,3-dioxides 2 , with a variety of substituents on the nitrogen atom, can be easily obtained by the title reaction. The isomeric compounds 4–6 are also formed from sulphonamides bearing an N-aralkyl group with a chain of two or more carbon atoms. Activation of the ring closure-position or deactivation of the aromatic ring in the substituent can direct the reaction to give compounds 2 . Cyclization results are influenced by the size of the new heterocycle ring and by the predominant formation of derivatives with the SO₂ group outside the ring.     

Microwave-assisted aza-Prins reaction. Part 1: facile preparation of natural-like 3-azabicyclo[3.3.1]non-6-enes

A facile and operationally simple route to diastereomerically pure, natural-like 3-azabicyclo[3.3.1]non-6-enes via microwave-assisted, BF₃·OEt₂-promoted aza-Prins reaction has been developed. Complexity-generating transformations based on these products involving reactive functionalities introduced during the aza-Prins step have been developed.     

Bicyclo[3.2.1]oct-6-enes via (3+2)cycloaddition

(3+2)Cycloaddition of alkynes to allyl cations, generated from 3-chlorocyclohexenes and zinc chloride, provides a simple and direct route to bicyclo[3.2.1]oct-6-enes.     

Rearrangements of 3-heterobicyclo[3.2.0]hept-6-enes

Studies directed at a synthesis of dihydrothiepin 1b have resulted in the elucidation of several factors which effect cyclobutene ring opening in the 3-heterobicyclo[3.2.0]hept-6-ene ring system. We report the unexpected rearrangement of 4a, 4b, 13b and 13c to the synthetically useful a-vinyl-2,5-dihydrothiophenes 7a, 7b, 15a and 15b, respectively. Conversion of 4a to 6 is suggested to occur by a 1,3-rearrangement of 4a to isomeric 3-thiabicyclo[3.2.0]hept-6-ene 19 followed by cyclobutene ring opening in 19.     

Intramolecular [2+2] photocycloaddition of 4-(allenic-substituted)-2-cycloalken-1-ones. Ring size,length of sidechain and temperature effects

The intramolecular [2+2] photocycloaddition of 4-(allenic-substituted)-2-cycloalken-1-ones has been shown to be controlled by the ring size of the cycloalkenone, the chain length and the temperature of the reaction.