Tetrahydrofurans, enantiomerically enriched

Cyclisation of a stereodefined organolithium derived from enantiomerically enriched a-alkoxy stannane 364 gave a tetrahydrofuran 365 with no loss of enantiomeric excess and with overall retention.153... 

Extension of the method to the synthesis of enantiomerically enriched tetrahydrofurans or tetrahydropyrans was possible by using chiral phosphine ligands on the gold catalyst. In the presence of chiral gold pre-catalyst [Au2 (.S)-3,5-r-Bu-4-MeO-MeOBIPHEP Cl2] and AgOTs, prochiral allenes afforded the desired heterocycles with high enantioselectivity (Scheme 4-101). 

Oxysulfenylation and oxyselenenylation of olefins, catalysed by chiral Brpnsted acids, have been reported to produce enantiomerically enriched tetrahydrofurans at <63% ee with dibenzoyl-tartaric acid and its derivatives as catalyst. Enantioselective desymmetrization of thiiranium and seleniranium ions (<50% and <84% ee, respectively) in the presence of chiral binaphthol-derived A(-triflyl phosphoramide as a catalyst has also been demonstrated. ... 

Nakai and coworkers90 have demonstrated that the carbanion cyclization of enantio-enriched a-(homoallyloxy)alkyllithiums, prepared from the corresponding stannanes 192, proceeds with complete retention of configuration at the lithium-atom-bearing carbon centre. The obtained tetrahydrofurans 193 are formed with high trans-selectivity and without losing the enantiomeric purity. This means that the lithium might coordinate to the... 

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