ALKYLATIONS OF (R,R)-2-TERT-BUTYL-6-METHYL-1,3-DIOXAN-4-ONES WHICH ARE NOT POSSIBLE WITH LITHIUM AMIDES MAY BE ACHIEVED WITH A SCHWESINGER-P4 BASE

Enolates A of the dioxanones specified in the title, when generated with lithium amide bases, can only be alkylated with highly reactive electrophiles, and only once. With Schwesinger's t-Bu-P4 base (a very strong, so-called neutral base, containing 4 P and 13 N atoms capable of bearing a positive charge in the conjugate P4H+ cation) the dioxanone 1 can be doubly alkylated even with iodobutane (products 16, 17). The 5,6-dimethyl- and 5-benzyl-6-methyldioxanone 2 and 3 can be alkylated diastereoselectively with the formation of quaternary centers at C(5) (products 4, 8 - 14). In one case, the configuration of the product 4 obtained was determined by conversion to a beta-lactone 6 and an olefin 7 (a previous assignment had to be revised). Even the 2,5,6,6-tetraalkyl-substituted dioxanone 19 could be further alkylated (--> 20 + 21). Five of the new alkylation products were hydrolyzed to the parent 3-hydroxy-carboxylic acids 5, 22 - 25. The enormous reactivities achieved with the inherently labile enolates and the P4H+ counterions are discussed.