The asymmetric catalytic addition of alcohols (phenols) to non-activated alkenes has been realized through the cycloisomerization of 2-allylphenols to 2-methyl-2,3-dihydrobenzofurans (2-methylcoumarans). The reaction was catalyzed by a chiral titanium-carboxylate complex at uncommonly high temperatures for asymmetric catalytic reactions. The catalyst was generated by mixing titanium isopropoxide, the chiral ligand (aS)-1-(2-methoxy-1-naphthyl)-2-naphthoic acid or its derivatives, and a co-catalytic amount of water in a ratio of 1:1:1 (5 mol % each). This homogeneous thermal catalysis (HOT-CAT) gave various (S)-2-methylcoumarans with yields of up to 90 % and in up to 85 % ee at 240 °C, and in 87 % ee at 220 °C.

An aluminum‐catalyzed intramolecular hydroalkoxylation of nonactivated alkenes is presented as a powerful synthetic tool for the preparation of oxygen heterocycles, which are of major interest for the preparation of biological and pharmaceutical active compounds. The aluminum isopropoxide catalyzed (5 mol %) cyclization of 2‐allylphenols at elevated temperatures (250 °C, 20 min) provides 2‐methylcoumarans (2‐methyl‐2,3‐dihydrobenzofuran) in an exceptionally fast, simple, and economic manner. Moreover, heating of allyl aryl ethers with aluminum isopropoxide (5 mol %) gives 2‐methylcoumarans by a tandem Claisen rearrangement–hydroalkoxylation reaction. For either reaction, the catalyst tolerates a broad scope of substrates with various functional groups. By using the weakly electrophilic aluminum alkoxide as the catalyst, occurrence of “hidden Brønsted acid” catalysis can be excluded under the present reaction conditions.

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Abstract:The asymmetric catalytic addition of alcohols (phenols) to non-activated alkenes has been realized through the cycloisomerization of 2-allylphenols to 2-methyl-2,3-dihydrobenzofurans (2-methylcoumarans). The reaction was catalyzed by ac hiral titanium-carboxylate complex at uncommonly high temperatures for asymmetric catalytic reactions. The catalyst was generated by mixing titanium isopropoxide, the chiral ligand (aS)-1-(2-methoxy-1-naphthyl)-2-naphthoic acid or its derivatives,a nd ac o-catalytic amount of water in ar atio of 1:1:1( 5mol %e ach). This homogeneous thermal catalysis (HOT-CAT) gave various (S)-2-methylcoumarans with yields of up to 90 %and in up to 85 %eeat240 8 8C, and in 87 %eeat2 20 8 8C.

Axially chiral, enantiopure 1,1′-binaphthyl-2-carboxylic acids (BINA-Cox) have recently been introduced as chiral ligands for transition metal catalysis. Together with equimolar, co-catalytic amounts of Ti(OiPr) 4 and water they form an in situ catalyst that performs the asymmetric catalytic hydroalkoxylation of 2-allylphenols to 2-methylcoumarans at high temperature (240°C, microwave heating). The synthesis of reference ligand 2′-MeO-BINA-Cox (L1) has been optimized and performed at molar scale. Synthetic routes have been developed to access a variety of substituted BINA-Cox ligands (>30 exam- [a]