Retro-synthetic analysis enantioselective

CPO has been used occasionally in complex syntheses. An important application of CPO as an enantioselective epoxidation catalyst is the efficient synthesis of (R)-2-mevalonolactone (Scheme 2.26a) [270]. A survey of the literature revealed that the previous methods required many steps to produce the lactone, in low overall yield, with moderate ee, in addition to expensive starting materials. Meanwhile, a retro-synthetic analysis starting with an appropriately functionalized epoxide provided confidence that CPO could rescue the situation if used in the key stereogenic step. Another completed synthesis is depicted in Scheme 2.26b. Again, the epoxide is generated in high yield with conversion to (R)-dimethyl-2-methylaziridine-l,2-dicarboxylate, which may serve as a synthon for P-methylamino acids [283],... 

As mentioned in the retro-synthetic analysis, the imine derivative 7 is the key intermediate of our enantioselective synthesis strategy. It was obtained by various pathways (Scheme 6.15) ... 

In 1998, Kawahara and Nagumo reported the first total synthesis of a member of the TAN1251 series [63] and five years later both authors revisited the TAN1251A alkaloid by means of a new enantioselective synthesis (see Section 5.6). The retro synthetic analysis of TAN 1251A is outlined in Scheme 37. The target compound could be obtained by aldol reaction of tricyclic lactam 119, whose disconnection at the amide bond led to the bicyclic amino acid 120, which could be prepared from azaspirocyclic compound 121 by means of alkylation of the secondary amine and Mitsunobu-type chemistry. Azabicycle 121 may be prepared by an intramolecular alkylation of 122, which in turn could be available from allyl derivative 123. The latter can be prepared from carboxylic acid 124 by alkylation and subsequent Curtius rearrangement. 

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