Search

Benzylation of chiral esters of N-acylglycines using various bases and additives was examined. No C-alkylation was observed with one equivalent of base. Diastereoselectivities were dependent on the amount of additive, the nature of the N-acyl group, and the chiral ester. A model to account for the degree and sense of the stereoselectivity is proposed.

Alkylations of anions derived from dipeptides with a glycine at the C-terminus have been investigated. A hydrocarbon sedition in the N-terminal residue does impart some asymmetric induction. The use of a chiral ester derivative provides the potential for double asymmetric induction and good selectivity. With an aspartyl residue at the N-terminus, problems were encountered due to competing side reactions. The use of an azetidinone could circumvent some of these, but the observed induction was not high.

Contrary to a published report, C-alkylation of methyl hippurate requires two equivalents of base. The choice of additive (TMEDA or HMPA) influences the result. Deuteration of the enolate gives results which depend on both the deuterium source and the nature of the additive.

Dissolving metal reduction of known enone S affords predominantly the racemic form of title ketone ( 3 ) whereas catalytic reduction gives the meso isomer 6 . Neither ketone 3 nor alcohol 4 could be satisfactorily resolved. Asymmetric synthesis of (−)− 3 and (+)− 4 (ee=91 %) was effected from ketone (+)- 13 .

Alkylation of the D-camphor imine of tert -butyl glycinate with secondary allylic and benzylic halides affords products which have high stereochemical purity, particularly at the halogen displacement site.

An improved synthesis of 1-azoniatricyclo[4.4.3.0 1,6 ]tridecane ( 2 ) and the preparation of the remaining member of the series, 1-azoniatricyclo[4.3.3.0 1,6 ]dodecane salts ( 3 ) have been achieved. Using a combination of 1 H (at 400 MHz) and 13 C NMR spectra has allowed the assignment of the signals in the well-resolved 1 H spectra. The results indicate that 1 exists in the all-chair form which undergoes racemization by ring inversion with a rate constant of 0.7 sec − and further that the counterion in these salts is restricted to associating with only one face of the tetrahedral N atom.

Attempted imine formation between 3-hydroxycamphor and tert. butyl glycinate led to 8 the substitution product at the 3-position. Zinc-acetic acid treatment of 8 afforded 3-acetoxycamphor. Alkylation of the imine from from norcamphor and tert. butyl glycinate gave no stereoselection. Alkylation of the imine from from 10-hytdroxymethylcamphor and tert. butyl glycinate gave stereoselectivities inferior to those obtained from the imine of camphor itself ( 1 ) but aldol condensation with benzaldehyde, a reaction not possible with 1, was affected in 71% yield.