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TiCl4-mediated aldol reactions of chiral methyl α-silyloxy ketones with a variety of aldehydes provide the corresponding 1,4-syn aldol adducts with moderate to high stereocontrol. This transformation represents a new approach to substrate-controlled acetate aldol reactions and complements the 1,4-anti asymmetric induction produced by the related α-benzyloxy ketones. This new approach could be useful in the design of more efficient syntheses of natural products.

A total synthesis of (+)-herboxidiene/GEX 1A has been accomplished from (R)- and (S)-lactate esters in a highly efficient manner. Key steps of the synthesis involve substrate-controlled titanium-mediated aldol reactions from chiral lactate-derived ethyl ketones, an oxa-Michael cyclization, an Ireland-Claisen rearrangement, and a Suzuki coupling. Furthermore, computational studies of the oxa-Michael reaction have unveiled the dramatic influence of intramolecular hydrogen bonds on the stereochemical outcome of such cyclizations, whereas biological analyses have clearly proved the important cytoxicity of (+)-herboxidiene/GEX 1A.

Good levels of 1,4-anti asymmetric induction are obtained in the TiCl3(i-PrO)-mediated aldol reaction of chiral α-benzyloxy methyl ketones with a wide array of aldehydes. This methodology represents a new approach to substrate-controlled acetate aldol reactions capable of providing highly functionalized fragments in a straightforward manner, which may be useful in the design of more efficient syntheses.

A sequential transformation based on a titanium-mediated aldol reaction from chiral α-tert-butyldimethylsilyloxy ketones followed by reduction of the resultant aldolates with LiBH4 provides a straightforward access to syn-1,3-diols. These diols, containing up to three new stereocentres, can be easily isolated in high yields after a simple work-up without any additional oxidative treatment, which confers to this procedure an appealing position to prepare stereoselectively such sort of structures.

Good levels of 1,4-syn asymmetric induction are obtained in the TiCl4-mediated aldol reaction of methyl α-silyloxy ketones with achiral aldehydes. Such methodology represents a new approach to the substrate-controlled acetate aldol reaction, which can be useful to design more efficient syntheses of natural products.

Substrate-controlled Michael additions of the titanium(IV) enolate of lactate-derived ketone 1 to acyclic α,β-unsaturated ketones in the presence of a Lewis acid (TiCl4 or SnCl4) provide the corresponding 2,4-anti-4,5-anti dicarbonyl compounds in good yields and excellent diastereomeric ratios. Likely, the nucleophilic species involved in such additions are bimetallic enolates that may add to enones through cyclic transition states. Finally, further studies indicate that a structurally related β-benzyloxy chiral ketone can also participate in such stereocontrolled conjugate additions.

Conversion of chiral N-acyl-4-benzyl-oxazolidinones (I) to titanium enolates and subsequent quenching with TEMPO results in an efficient formation of 2-aminoxylation adducts in excellent yields and good enantioselectivities.

Good levels of 1,4- anti asymmetric induction are obtained in the TiCl 3 ( i -PrO)-mediated aldol reaction of α-benzyloxy methyl ketones with achiral aldehydes. Such methodology represents a new approach to the substrate-controlled acetate aldol reaction, which can be useful to design more efficient synthesis.

A highly efficient and straightforward aminoxylation of titanium(IV) enolates from (S)-N-acyl-4-benzyl-5,5-dimethyl-1,3-oxazolidin-2-ones with TEMPO has been developed. A wide array of functional groups on the acyl moiety, including alkyl and aryl substituents, olefins, esters, or a-cyclopropyl, as well as a-trifluoromethyl groups, are well tolerated. This transformation can therefore produce the a-aminoxylated adducts in excellent yields with high diastereomeric ratios (d.r.). In turn, parallel additions to the a,b-unsaturated N-acyl counterparts give the corresponding g-adducts with complete regioselectivity in moderate to good yields. Removal of the piperidinyl moiety or the chiral auxiliary converts the resultant adducts into enantiomerically pure a-hydroxy carboxyl derivatives, alcohols, or esters in high yields under mild conditions. Finally, a new mechanistic model based on the biradical character of the titanium(IV) enolates has been proposed.

Substrate-controlled Michael additions of the titanium-(IV) enolate of lactate-derived ketone 1 to acyclic α,β-unsaturated ketones in the presence of a Lewis acid (TiCl4 or SnCl4) provide the corresponding 2,4-anti-4,5-anti dicarbonyl compounds in good yields and excellent diastereomeric ratios. Likely, the nucleophilic species involved in such additions are bimetallic enolates that may add to enones through cyclic transition states. Finally, further studies indicate that a structurally related β-benzyloxy chiral ketone can also participate in such stereocontrolled conjugate additions.

The titanium-mediated aldol reaction of chiral ketones is sensitive to the titanium Lewis acid used in the enolization step and represents a new approach to the substrate-controlled acetate aldol reaction.

A substrate-controlled synthesis of (+)-herboxidiene from two lactate-derived chiral ketones is described. Remarkably, most of the carbon backbone was constructed through highly stereoselective titanium-mediated aldol reactions and an Ireland–Claisen rearrangement. Furthermore, an oxa-Michael cyclization and a high-yield Suzuki coupling were used to assemble the pyran ring and the diene moiety respectively.

A sequential transformation based on a titanium-mediated aldol reaction from chiral α-tert-butyldimethylsilyloxy ketones followed by reduction of the resultant aldolates with LiBH4 provides a straightforward access to syn-1,3-diols. These diols, containing up to three new stereocentres, can be easily isolated in high yields after a simple work-up without any additional oxidative treatment, which confers to this procedure an appealing position to prepare stereoselectively such sort of structures.

Good levels of 1,4-syn asymmetric induction are obtained in the TiCl4-mediated aldol reaction of methyl α-silyloxy ketones with achiral aldehydes. Such methodology represents a new approach to the substrate-controlled acetate aldol reaction, which can be useful to design more efficient syntheses of natural products.

Good levels of 1,4- anti asymmetric induction are obtained in the TiCl 3 ( i -PrO)-mediated aldol reaction of α-benzyloxy methyl ketones with achiral aldehydes. Such methodology represents a new approach to the substrate-controlled acetate aldol reaction, which can be useful to design more efficient synthesis.