Cycloaddition–hydrogenolysis strategy for the synthesis of 2,4-disubstituted pyroglutamates

Substituted proline derivatives as organocatalysts in Michael reaction

“…Compounds 3, 17 and 21 were synthesised according to the literature procedures. 10,11 General procedure for the cycloaddition reactions A mixture of the imine (l eq. ), triethylamine (0.25 eq.…”

“…( (11). Flash chromatography (SiO 2 , 4:6 V/V petroleum ether-diethyl ether) afforded the product as a yellow amorphous solid (m.p.…”

Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

“…In addition, the lactamized derivatives of these compounds, pyroglutamates, occur in a number of well-known biologically active natural products including dysibetaine [6][7][8][9][10][11][12], salinosporamide A [13][14][15][16][17][18], and lactacystin [19][20][21][22] (Figure 1). Accordingly, efficient procedures to access α-substituted glutamates and pyroglutamates in enantioenriched form have been the target of numerous reports [23][24][25][26][27].…”

A Facile Cu(I)/BINAP-Catalyzed Asymmetric Approach to Functionalized Pyroglutamate Derivatives Bearing a Unique Quaternary Stereogenic Center

“…For example, oxazolomycin A and lactacystin were isolated from the fermentation broth of Streptomyces sp , and salinosporamide A was isolated from a marine actinomycete Salinispora tropica (Figure ). These optically active pyroglutamates bearing a quaternary stereogenic center exhibit a broad array of important biological and potentially valuable pharmaceutical properties, which have inspired organic chemists to pursue efficient synthetic methods for those compounds in recent years …”

“…Although there are elegant and creative strategies toward the construction of a pyroglutamate architecture, the directly catalytic asymmetric approach to access optically pure pyroglutamate bearing a quaternary stereogenic center has met with little success . To the best of our knowledge, only one noncatalytic and nonasymmetric example has been reported for the synthesis of pyroglutamate derivatives containing a quaternary stereogenic center via stoichiometric LiHMDS-mediated tandem Michael addition–elimination of α-substituted aldimino esters with Morita–Baylis–Hillman (MBH) carbonates followed by a deprotection/lactamization protocol(Scheme ).…”