A Route to Carbasugar Analogues - Jonathan Clayden - The ...

1.3 – Nucleophilic dearomatisation
For such a small change in conditions regioselectivity is very high, presumably
because the addition remains under thermodynamic control. This was supported when
lithium amides from Table 1.10 were re-subjected to the new conditions still gave 1,4-
adducts. Diastereoselectivities were somewhat less than the previous 1,4-additions, as
would be expected for the formation of such distant stereocentres. Unlike the 1,4-
additions, DMPU did not promote reaction, and adducts 62 were used in the synthesis
of δ-amino acids. 41
1.3.3 Catalytic systems
The above systems have been specific to a single functional group which remains in
the product. Whilst this may be acceptable if that functionality is desired, or can easily
be removed, it places significant restriction on synthetic design. In principle, a
generally applicable catalytic methods offers clear advantages over a comparable
stoichiometric process.
1.3.3.a Bulky Lewis acid
In a series of communications, Yamamoto and Saito have achieved dearomatising
additions to aromatic ketones, 42 aldehydes, 42 acid chlorides 43 and esters. 44 This has
been accomplished by the use of the “carbonyl protector” ATPH (Table 1.12)
promoting 1,6-addition by acting as a Lewis acid and preventing direct addition to the
electron withdrawing group.
36