Addition of Substituted Allyltitanium Reagents to Aldehydes and Ketones

3 Addition of Substituted Allyltitanium Reagents to Aldehydes and Ketones 

The best results affre obtained by using Sato s sandwich compounds 223 119). However, the nature of the ligands in reagents of the type 219-220 have not been varied systematically. 

Quenching the anion 225 with titanium tetraisopropoxide 2 affords the ate complex 226, which reacts 100% regio- and distereoselectively with aldehydes to afford the threo adducts 227 ( 95% conversion, 80% isolated by distillation)90) (Equation 71). This methodology is simpler than analogous reactions of boron reagents122). Furthermore, even ketones react threo-selectively (Equation 72)90). Since the adducts can be converted by adds (anti elimination) or KH (syn elimination) into the two possible diastereomeric dienes122), the sequence is synthetically useful. 

Finally, recent application of organotitanium chemistry to the problem of stereoselective homoaldol condensation (Equation 73) turned out to be highly successful, as reported by Hoppe 123). The threo/erythro ratios (232 233) were better than 97 3 for various aldehydes. 

Enantioselective Addition of Chirally Modified Organotitanium Reagents to Carbonyl Compounds 

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