Thermodynamic control carbonyl basicity

Notice the control inherent in the aldol cyclisation. One from four possible enolates attack one of two carbonyl compounds. This is clearly thermodynamic control under these weakly basic conditions (chapter 5 ). The more highly substituted alkene (here tetra-substituted) and the most stable possible ring (i.e. 5- not 3- or 4-membered) is formed. The geometry of the alkene is of course controlled by the ring.20... 

Kinetics Proton transfer catalyzes many reactions. Proton transfer between heteroatom lone pairs is very fast, often at the diffusion-controlled limit. Under reversible (equilibrium) conditions, the most acidic proton is removed preferentially. However, if the deprotonation is done under irreversible conditions, the proton removed is determined by kinetics, not thermodynamics (Section 9.3). Anion basicity always competes with nucleophilicity. Proton transfer is slow enough between organometallics and protons adjacent to carbonyls (carbon bases with carbon acids) that addition of the organometallic to the carbonyl is the dominant process, path AdN. 

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