Enantioselectivity, coupling with allylic carbonates

Distal C-C bond formation can also be used to construct cyclic ethers, but this demands that methods be developed for the enantioselective assembly of complex acyclic ethers. P. Andrew Evans of Indiana University has demonstrated (Angew. Chem. Jnt. Ed. 2004, 43,4788) that Rh-mediated coupling of secondary allylic carbonates such as 7 with secondary alcohols such as 8, both enantiomerically pure, proceeds with clean retention (double inversion) of absolute configuration. Alkene metathesis then delivers the cyclic ether 9 in high diastereomeric and enantiomeric purity. 

AUylation of a camphorsultam-modified glycine derivative 26 proceeds on deprotonation and addition of a Pd catalyst and an allyl carbonate. A three-component coupling involving a-allylation of A-acryloyloxazolidin-2-one by reactions with free radicals is rendered enantioselective in the presence of a bis(4-phenyloxazoline)methane ligand analogous to 12. Similarly, a stepwise Baylis-Hillman reaction to furnish chiral a-methylene-P-hydroxy ketones is effective if catalyzed by a tartaric acid derivative 27. 

Hojoh K, Shido Y, Ohmiya H, Sawamura M (2014) Construction of quaternary stereogenic carbon centers through copper-catalyzed enantioselective allylic cross-coupling with alkylboranes. Angew Chem Int Ed 53 4954-4958... 

Cozzi employed stereoselective CDC reactions promoted by DDQ and the MacMillan catalyst 133 (Scheme 8.65). Various compounds having a benzylic and/or allylic carbon can be converted into the corresponding C-C coupling products 134-137 in low-to-moderate yields with moderate-to-high enantioselectivities. 

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