Types of Additional Functional Groups Tolerated

Aldehydes 39a-g — 54 react smoothly with methyltitanium triisopropoxide 6 (the numbers in parentheses refer to yields of isolated adducts). Generally, a 10-15% excess of titanium reagent is used, except in compounds containing HO-groups (100% excess). In case of a, P-unsaturated carbonyl compounds, the 1,2-addition mode is observed 22,76,82). 

The methylation of pregnenolone acetate 58 to form 59 occurs chemoselectively with 6 83). The zirconium reagent 61, prepared by quenching methyllithium with 60, reacts analogously83), so that no advantages are apparent in this case. 

Cyano or chloromethyl groups also do not interfere with carbonyl addition. Dimethyltitanium diisopropoxide 6321), easily accessible from 62 84), reacts chemoselectively with 64 to form 55 (95%)82 63 is considerably more reactive than 

4 A single diastereomer resulting from preferential equatorial attack is formed. Stereoselectivities are discussed in detail in Section D.II, 

Hesse s report8S) that 72 is smoothly methylated by 6 (85 % 73) also demonstrates that incompatibility of aliphatic nitro groups with organotitanium reagents is not general. In this case a more reactive aldehyde function is involved. As already stressed, ketones react much more slowly than aldehydes, so that side reactions 

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