Synthesis of four diastereomers of notoryne and their 13C NMR chemical shifts analysis

In this manuscript we document the details of the synthesis of four diastereomers of notoryne. The synthesis of one of the diastereomer having a similar relative stereochemistry of substituents on the both THF rings like notoryne, however, being the relative stereochemistry between the bridging carbon of these two THF units is changed from anti to syn has been executed mainly to learn how the ring carbon chemical shifts vary with this change. Interestingly, the deviations are found mainly for the carbons of THF ring that bears the Br-group. In addition to this isomer, three more diastereomers having the relative stereochemistry of substituents on either of the THF rings varied have been also synthesized. All four diastereomers have been subjected for extensive NMR studies and their 13 C NMR chemical shifts have been compared with notoryne and laurendecumenyne B. In addition, chemical shifts for the four diastereomers along with these natural products were calculated with the help of DFT calculations and compared to the experimentally obtained chemical shift values. The notoryne diastereomer 1 having similar relative stereochemistry of substituents on both THF rings and being the relative stereochemistry between the bridging carbon of these two THF units is changed from anti to syn, has been executed to learn how the ring carbon chemical shifts vary with this change. Also, the three other diastereomers 2–4 have been synthesized and a detailed NMR analysis has been carried out/compared.