Lignocellulosic biomass pyrolysis with acid catalysis selectively produces the useful chiral synthon 6,8-dioxabicyclo[3.2.1]oct-2-ene-4-one ((–)-levoglucosenone, LGO). In this report, LGO was used to prepare (3R,5S)-3-benzyl-5-(hydroxymethyl)-4,5-dihydrofuran-2(3H)-one, which is an intermediate used in the construction of antivirals including the protease inhibitor indinavir. To achieve the synthesis, the hydrogenated derivative of LGO was functionalised using aldol chemistry and various aromatic aldehydes were used to show the scope of the reaction. Choice of base affected reaction times and the best yields were obtained using 1,1,3,3-tetramethylguanidine. Hydrogenation of the α-benzylidene-substituted bicyclic system afforded a 4 : 3 equatorial/axial mixture of isomers, which was equilibrated to a 97 : 3 mixture under basic conditions. Subsequent Baeyer–Villiger reaction afforded the target lactone in 57 % overall yield for four steps, a route that avoids the protection and strong base required in the traditional approach. The aldol route is contrasted with the α-alkylation and a Baylis–Hillman approach that also both start with LGO.
The synthesis of tri- and tetrasubstituted cyclopropanes from 3-aryl-substituted levoglucosenones (LGO) has been developed. In contrast to the unstabilised ylide dimethylsulfonium methylide which gives epoxides from LGO via 1,2-addition, we have found that the soft nucleophile dimethylsulfoxonium methylide affords cyclopropanes in moderate yields from LGO and in excellent yields and stereoselectivity with 3-aryl LGO derivatives. The use of 1,1,3,3-tetramethylguanidine as base in DMSO to generate the ylide provided the best yields and shortest reaction times. Ester stabilised sulfonium ylides could also be used to generate tetrasubstituted cyclopropane derivatives. One of the products was converted into a cyclopropyl lactone via Baeyer–Villiger oxidation to demonstrate the utility of applying cyclopropanation chemistry to LGO.
Chiral amines are highly coveted within the fine‐chemical industry and sustainable synthetic methodologies for their production are of great value. By harnessing the chirality present in cellulose‐derived (–)‐levoglucosenone (LGO), several bio‐based sp3‐rich amines containing up to four chiral centres have been readily prepared under aqueous conditions without using any catalysts, ligands, auxiliaries or resolutions.
Efficient conditions have been developed for the diastereoselective aziridination of the biomass pyrolysis product (−)-levoglucosenone, via the reaction of primary aliphatic amines with 3-iodolevoglucosenone. In contrast to the reactions of aliphatic amines, the use of 4-methoxyaniline resulted in an aza-Michael-initiated dimerisation reaction, and 1,3-diphenylurea gave a 2-imidazolidinone. The aziridine products were transformed using the aza-Wharton reaction, affording novel sulfonamide and amine-substituted 6,8-dioxabicyclo[3.2.1]oct-3-enes with potential as sp3-rich chiral scaffolds.
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