Search

Interaction of titanium(IV) isopropoxide with ethylmagnesium bromide and its higher homologs leads to the generation of alkoxytitanacyclopropane species, which are able to act in the reactions with unsaturated compounds as 1,2-dicarbanionic alkylating agents. The present review is focused on the processes of intermolecular regio- and stereoselective alkylation of carboxylic esters and allylic alcohol derivatives with alkoxytitanacyclopropane reagents. The oxophilicity of the titanium atom and its tendency to form sterically crowded ate complexes are probably the main factors providing a high level of selectivity of these transformations. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 269–278; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20155

Reaction of homoallylic alcohols 1a-e with i-PrMgBr in the presence of Ti(i-PrO) 4 leads to the unbranched saturated diols 2a-e as the main products in moderate to good yields. The head-to-head regioselectivity in reductive coupling of 4-penner-1-ol and 5-hexen-2-ol was also observed. Coupling of 2-methyl-5-hexen-2-ol, as well as unsaturated alcohols in which vinyl and hydroxyl groups are more distant from one another, proceeded with head-to-tail or tail-to-tail regioselectivity. It is supposed, that the unusual head-to-head regioselectivity in reductive coupling of homoallylic alcohols 1a-e is due to the formation of the key titanacyclopentane intermediates F and G having two fused oxatitanacyclopentane rings.

In the presence of Ti(Oi-Pr)4 reaction of EtMgBr with allylic alcohols and allylic ethers affords the products of formal SN2′ substitution of hydroxy or alkoxy groups with ethyl groups in moderate to good yields and excellent regioselectivity. The mechanism of the reaction includes the formation of titanacyclopropanes as the key organometallic intermediates. Promoting action of EtMgBr on the process of C-C bond formation in the transformation of titanacyclopropane-olefin complex 5 into the titanacyclopentane at complex 6 is proposed.

The regioselective two-step sequence of bromination-dehydrobromination of 2-(2,2-diethoxy)-1-methyl-1-cyclopropanol affords 3-(2,2-diethoxyethyl)-3-buten-2-one in high yield. The reduction of the latter, followed by chlorination and dehydrochlorination, provides 2-(2,2-diethoxyethyl)-1,3-butadiene that was used as a building block for the synthesis of (±)-ipsenol, (±)-ipsdienol and amitinol - the components of aggregation pheromones of the Ips bark beetles.

Allylic ethylation of 2-((E)-dodec-2-en-4-yloxy)tetrahydro-2H-pyran with ethylmagnesium bromide in the presence of titanium(IV) isopropoxide proceeds via a SN2′ pathway to afford (E)-3-methyltridec-4-ene with excellent syn-diastereoselecivity. This transformation is used as a key step in the synthesis of (1R/S,7R)-1,7-dimethylnonyl propanoate, the Western corn rootworm (Diabrotica virgifera virgifera) sex attractant.

A convenient new approach to the synthesis of the C13–C21 epothilone fragment using the cyclopropanation of the ethoxycarbonyl groups in O-THP protected diethyl (S)-malate with ethylmagnesium bromide in the presence of titanium(IV) isopropoxide followed by site-selective cyclopropane cleavage as the key steps has been performed.

Interaction of titanium(IV) isopropoxide with ethylmagnesium bromide and its higher homologs leads to the generation of alkoxytitanacyclopropane species, which are able to act in the reactions with unsaturated compounds as 1,2-dicarbanionic alkylating agents. The present review is focused on the processes of intermolecular regio- and stereoselective alkylation of carboxylic esters and allylic alcohol derivatives with alkoxytitanacyclopropane reagents. The oxophilicity of the titanium atom and its tendency to form sterically crowded ate complexes are probably the main factors providing a high level of selectivity of these transformations. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 269–278; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20155

Reaction of homoallylic alcohols 1a-e with i-PrMgBr in the presence of Ti(i-PrO) 4 leads to the unbranched saturated diols 2a-e as the main products in moderate to good yields. The head-to-head regioselectivity in reductive coupling of 4-penner-1-ol and 5-hexen-2-ol was also observed. Coupling of 2-methyl-5-hexen-2-ol, as well as unsaturated alcohols in which vinyl and hydroxyl groups are more distant from one another, proceeded with head-to-tail or tail-to-tail regioselectivity. It is supposed, that the unusual head-to-head regioselectivity in reductive coupling of homoallylic alcohols 1a-e is due to the formation of the key titanacyclopentane intermediates F and G having two fused oxatitanacyclopentane rings.

In the presence of Ti(Oi-Pr)4 reaction of EtMgBr with allylic alcohols and allylic ethers affords the products of formal SN2′ substitution of hydroxy or alkoxy groups with ethyl groups in moderate to good yields and excellent regioselectivity. The mechanism of the reaction includes the formation of titanacyclopropanes as the key organometallic intermediates. Promoting action of EtMgBr on the process of C-C bond formation in the transformation of titanacyclopropane-olefin complex 5 into the titanacyclopentane at complex 6 is proposed.