(equation presented) A new general route to U-type cavity structures (molecular clefts) with inside functionality has been developed using wall extension or base/ roof assembly methods which draw upon (i) the 1,3-dipolar cycloaddition reaction between alkenes and cyclobutene epoxides (ACE coupling) or (ii) the Diels Alder reaction of alkenes with fused dihydropyridazines (s-tetrazine coupling). In this way, functional units (e.g., crown ethers, redox-active naphthalenes) have been attached stereospecifically to short-walled bis-alkenes 1-5 to produce cavity structure 6-10 with top-of-wall separations (C to C) from 4.5 to 12.7 Å.