Crossed or mixed aldol reactions

These reactions involve two different carbonyl partners. If two similar aldehydes or ketones are reacted, a mixture of all four possible products is formed (e.g. reaction of A and B gives AA, AB, BA and BB). This is because both carbonyl partners can act as nucleophiles and electrophiles. 

Slow addition of BuCOCH3 (to PhCHO/ hydroxide) means that as soon as the enolate is generated, it is trapped by PhCHO and not BuCOCH3 (as this is present in low concentration) O O H 1 II ph X Bu H H H /  

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