Intramolecular [2 + 2] Photocycloaddition of Alkenes Incorporated in a Carbohydrate Template. Synthesis of Enantiopure Bicyclo[3.2.0]heptanes and -[6.3.0]undecanes

Abstract

Intramolecular [2 + 2] photocycloaddition of alkenes with a furano sugar placed between them have been investigated under both copper(I)-catalyzed and sensitized conditions. The copper(I)-catalyzed photocycloaddition of the dienes 4a, 4b, and 4c led to unexpected formation of the thermodynamically less stable cis-syn-cis 4-5-5 tricyclic adducts 5a, 5b, and 5c, respectively. The sensitized photocycloaddition of the diene 14 also gave the cis-syn-cis adduct 15 showing that the copper(I) catalyst does not have any influence on the stereochemical course through coordination with the anomeric ring oxygen of the furano sugar. The identical stereochemical course observed under both catalyzed and sensitized photoaddition reactions have been attributed to be of steric origin. Bis(dienes) 25a and 25b, which gave an intractable mixture on copper(I)-catalyzed irradiation, underwent smooth photocycloaddition in the presence of benzophenone, and the resulting 1,2-divinyl cyclobutanes underwent spontaneous [3.3]-rearrangement at room temperature to produce bicyclo[6.3.0]undecanes 30a and 30b, respectively. This investigation provides an approach for the construction of enantiopure bicyclo[3.2.0]heptanes and -[6.3.0]undecanes.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…A chiral auxiliary approach was more successful with a diastereomeric excess ( de ) of up to 60% . The extensive pool of chiral enantiomerically pure compounds accessible from carbohydrates has been exploited by the Ghosh and Jenkins group to produce an array of new fused and spiro annulated structures by a Cu­(I)-catalyzed [2 + 2] photocycloaddition. − Scheme illustrates an application of these experiments to the synthesis of new carbohydrate-type products 36 derived from precursors 35 .…”

Intramolecular Diels‐Alder Approach to the Construction of Fused Bicyclic 8/6 Ring System of Variecolin

“…The feasibility of bicyclo annulation on to a carbohydrate derivative through IMDA reaction was initially tested by the synthesis of decalin derivatives as depicted in Scheme 2. Reaction of vinyl magnesium bromide with the aldehyde 5 a prepared from the ketone 4 using the procedure developed earlier from this laboratory [23] afforded a 1 : 1 inseparable diastereoisomeric mixture of the carbinols 6 a in 65 % yield.…”

Efficient Synthetic Routes to (±)‐Hippolachnin A, (±)‐Gracilioethers E and F and the Alleged Structure of (±)‐Gracilioether I

“…However, the subsequent intramolecular photo‐induced [2+2] cycloaddition of 21 did not occur as expected; irradiation with UV light (mercury lamp) resulted in only configurational change of the C−C double bond in the side‐chain. Interestingly, the non‐conjugated alkene 20 underwent the photo‐induced intramolecular [2+2] cycloaddition smoothly in the presence of CuOTf⋅PhH to afford 22 (an advanced intermediate in Carreira's synthesis of hippolachinin A 7 ), although the yield was not very good and the reaction was rather slow (48 h).…”