Sterically congested macrobicycles with heteroatomic bridgehead functionality

Chiral Polyaryl Cyclophanes

“…The resolved compounds 2 and 4 do not exhibit exceptional chiroptical properties; for example, (+)‐ and (–)‐ 4 display [ α ] D = +131 and [ α ] D = –122, respectively . However, the computational studies reported herein indicate that if acenes could be substituted for the simple benzene rings in the capping propellers of such molecules, then the specific rotations would be much larger, and other chiroptical properties might be more extreme as well.…”

“…Over the last 25 years, we have prepared numerous triarylelement‐capped in ‐cyclophanes (such as compounds 1 – 3 ) and, more recently, a series of related in,in ‐cyclophanes (e.g. 4 ).…”

“…[2b] Its nitro derivative 2 was resolved and found to be configurationally stable under ordinary conditions, but no experimental Δ G ‡ rac was determined. Much later, the in,in ‐cyclophane 4 was resolved, and no racemization of pure (–)‐ 4 was observed upon heating for 24 h at 100 °C, indicating that Δ G ‡ rac > 31 kcal/mol, but complete decomposition occurred upon heating for 24 h at 180 °C . It has proven difficult to characterize the racemization pathways by computational studies, but B3LYP/6‐31G(d) calculations for compound 3 did yield a clearly defined, two‐step racemization path with Δ G ‡ rac = 63 kcal/mol, far too high for easy experimental measurement (due to decomposition).…”

in,in-Cyclophanes with Bridgehead Methyl Groups

“…During the last five years, we have synthesized numerous in,in -cyclophanes ( 1 ) with a wide variety of inwardly directed functional groups at their bridgeheads. These include C–H, N-lp (lp = lone pair), Si–H, Si–OH, Si–F, P-lp, and P–H, as well as one example of metal encapsulation by inwardly directed lone pairs (P–Ag–P). − Some of these compounds display extraordinarily short hydrogen–hydrogen nonbonded contact distances, , and others display unusual through-space spin–spin coupling in their NMR spectra. ,− …”

“…Cyclophane 3 is formed in very low yield by the reaction of tris­(2-mercaptophenyl)­methylsilane ( 7 ) and commercial 1,4-bis­(chloromethyl)­benzene ( 8 ), but the two-step procedure illustrated in Scheme is far superior, if not high-yielding. Compound 7 was first treated with an excess of 8 to give the triple adduct 9 in 60% yield after purification, and then condensation of 9 with another molecule of 7 at high dilution gave the dimethyl cyclophane 3 in 5% yield.…”