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[reaction: see text] An unprecedented copper phosphoramidite catalyzed enantioselective alkylative ring-opening reaction of oxabenzonorbornadiene derivatives with dialkylzinc reagents is reported. The reaction shows high levels of anti-stereoselectivity (up to anti/syn >99:1), complementary to the Pd(0)-catalyzed syn-selective ring-opening protocol, allowing a new entry to anti-dihydronaphthols with high enantioselectivity (up to 99% ee).

The regioselective ring opening of 2-aryl-substituted four-membered heterocyclic rings with phenols, including catechol, was achieved by the use of aryl borates in mild and neutral reaction conditions without the aid of any transition metal catalysts. While N-alkyl azetidines were found not to be reactive, optically active N-tosyl azetidines gave the corresponding beta-aryloxy amines in a racemic form, thus indicating the considerable carbocationic character of the transition state. The introduction of a hydroxyl group in the azetidine ring (i.e., an azetidinol), able to anchor the aryl borate and to direct the subsequent nucleophilic delivery, was shown to determine the ring-opening process with predominant inversion of configuration. When enantiomerically enriched 2-aryl oxetanes were used, the reduced extent of racemization observed (up to 93:7 er) was rationalized by an intramolecular delivery through a six-membered transition state, giving beta-aryloxy alcohols with a predominant retention of configuration (i.e., a syn-stereoselective ring opening). The aryloxy alcohols obtained, endowed with suitable functionalities, can be cyclized to give access to enantiomerically enriched 2-aryl-1,5-benzodioxepins.

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Chiral recognition leads to enantio‐ and regiodivergent reactivity: An unusual regiodivergent catalytic kinetic resolution has been accomplished for the first time in an organometallic reaction in which a C−C bond is formed. Chiral copper complexes of the non‐racemic phosphoramidite ligand L* discriminate the enantiomers of semirigid vinyloxiranes (having a blocked s‐cis or s‐trans conformation) to give separable regioisomeric products with very high stereocontrol in a two‐step process (see scheme).

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In order to study the effect of a remote polar functionality on the regiochemistry of the ring opening of aliphatic epoxides, the synthesis and some nucleophilic additions (methanolysis, azidolysis, and aminolysis) of suitable 2,3-epoxy-l-alkanol derivatives (epoxides trans-la4 and cis-2) were carried out. The C-3 selectivity commonly observed when nonchelating ring opening conditions are used is lower than when the epoxides are allowed to react in the presence of metal ions (Li+, Mg2+, Zn2+) due to the probable intervention of bidentate-chelated intermediates in the latter case, and in some instances an almost complete C-3 regioselection is obtained. Under identical conditions involving chelation control, trans epoxide la shows higher C-3 selectivity than cis isomer 2. A free hydroxyl functionality is not necessary in order to observe chelation-controlled regioselectivity in the epoxides that we examined.