Abstract
The 2,4-pentanediol (PD)-tethered Buchner reaction, cycloaddition of a carbenoid with an aromatic ring, produces stereochemically pure cycloheptatriene analogues in high yields. When the aromatic ring has meta-substituent, the tether also sufficiently controls the regiochemistry of the addition irrespective of the electronic nature of the meta-substituents to give a single product. The regioselectivity can also observed in the reaction with a 3,5-disubstituted substrate, in which isopropyl and methyl substituents were moderately differentiated with Rh2(OAc)4 catalyst to give a regioisomeric mixture in a ratio of 3:1. The catalyst having bulkier ligands such as triphenylacetyl resulted in 100:1. Synthetic utility of this highly regioselective as well as stereoselective reaction is also presented. The regioselectivity is attributed to steric effects, which are proved by the measurement of the addition rates as effective molarities. Hammett relation of the reactivities is also presented.
