Desymmetrisation of meso-methylcyclooctanones. Highly enantioselective synthesis of C8 syn-isoprenoid and syn,syn-deoxypropionate subunits from a bicyclo[3.3.1]nonane precursor

Different routes for the construction of biologically active diversely functionalized bicyclo[3.3.1]nonanes: an exploration of new perspectives for anticancer chemotherapeutics

Cancer is the second most high-morbidity disease throughout the world. From ancient days, natural products have been known to possess several biological activities, and research on natural products is one of the most enticing areas where scientists are engrossed in the extraction of valuable compounds from various plants to isolate many life-saving medicines, along with their other applications. It has been noticed that the bicyclo[3.3.1]nonane moiety is predominant in most biologically active natural products owing to its exceptional characteristics compared to others. Many derivatives of bicyclo[3.3.1]nonane are attractive to researchers for use in asymmetric catalysis or as potent anticancer entities along with their successful applications as ion receptors, metallocycles, and molecular tweezers. Therefore, this review article discusses several miscellaneous synthetic routes for the construction of bicyclo[3.3.1]nonanes and their heteroanalogues in association with the delineation of their anticancer activities with few selective compounds.

Straightforward Synthesis of Chiral Terpenoid Building Blocks by Ru-Catalyzed Enantioselective Hydrogenation

Starting from commercially available (R)- and (S)-β-citronellol, two strategies were designed to synthesize all four stereoisomers of 2,6-dimethyloctane monoterpene chirons in four or five steps in 32-47% overall yield. The desired fragments were obtained by a key Ru-catalyzed asymmetric olefin hydrogenation step under moderate temperature (50 °C), pressure (4 bar), and low catalyst loadings (0.5 mol %) under optimized conditions. Screening of commercially available catalysts highlighted the key role of DM-SEGPHOS as an economically advantageous alternative to commonly used H8-BINAP for equal performances. These results open new possibilities for versatile and scalable syntheses of these useful building blocks.

Stereochemical investigation on the construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of 2-cyclohexenones

A method for the practical construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of cyclohexenones with acrylates using K2CO3 and TBAB (n-Bu4N+ Br-) was developed. The construction could be carried out in both stepwise and one-pot reactions with similar tendencies in regioselectivity. The alpha-regioselectivity in the intramolecular Michael reaction agreed with that stereoelectronically expected in intermolecular reactions based upon consideration of the HOMO orbital profile of the enolate I, the precursor to ring-closure, although the reaction site was trisubstituted and prone to steric hindrance in most of the examples presented. For the acetoxymethylacrylates substituted at either the alpha or gamma position, steric hindrance of the substituents (R2 and R3) served as a controlling factor to induce high regiocontrol. Facial selection in the protonation of enolate II, formed upon ring-closure, was also affected by these substituents. In both the intramolecular Michael reaction and the protonation of enolate II, the ammonium counter cation played an important role.

Catalytic asymmetric synthesis of enantiopure isoprenoid building blocks: application in the synthesis of apple leafminer pheromones

The first catalytic asymmetric procedure capable of preparing all 4 diastereoisomers (ee > 99%, de > 98%) of a versatile saturated isoprenoid building block was developed and the value of this new method was demonstrated in its application to the concise total synthesis of two pheromones.

Total synthesis of the cytotoxic cyclodepsipeptide (-)-doliculide: the "ester" effect in acyclic 1,3-induction of deoxypropionates

The total synthesis of the marine cyclodepsipeptide (-)-doliculide is described. An acyclic (2S,4S,6R)-trimethyl alkanoic acid precursor to the "hydrocarbon" portion of doliculide was synthesized starting with l-ascorbic acid based on a stereocontrolled iterative conjugate addition of lithium dimethylcuprate to acyclic delta-Cmethyl alpha,beta-unsaturated ester derivatives. syn/syn selectivity was achieved by relying on 1,3-induction in preferred folded conformations that avoid 1,5-syn-pentane interactions in the transition states. The nature of the ester moiety seems to play an important role in determining the syn/anti ratios of C-methyl adducts. The 1-methyl-1-cyclopentyl ester group was found to confer the best syn selectivity to the cuprate addition products, especially in seven-carbon enoates.

A catalytic and iterative route to β-substituted esters via highly enantioselective conjugate addition of dimethylzinc to unsaturated malonates

Using the chiral phosphoramidite ligand (S,R,R)-L1 in the conjugate addition of dimethylzinc to acyclic unsaturated malonates, enantioselectivities of up to 98% have been obtained for the first time. An iterative and stereodivergent route to 3,5-dimethyl esters that takes advantage of this asymmetric catalysis has been developed.