First Practical Protection of α-Amino Acids as N,N-Benzyloxycarbamoyl Derivatives

Abstract

The consecutive treatment of N-Cbz amino protected compounds with LiHMDS and CbzCl provides a practical method for the preparation of N,N-benzyloxycarbamoyl (N,N-di-Cbz) derivatives in good yield. When alpha-amino acids are used the protection occurs without racemization. The method is compatible with a wide range of other functional and protecting groups. The procedure is also valid for the synthesis of mixed N,N-carbamoyl derivatives.

Silyl Group‐Directed 6‐exo‐dig Iodocyclization of Homopropargylic Carbamates and Amides

“…The ozonolysis of 5 also led to 4 in 59 % yield. Each specific rotation of 4 is identical with that of literature . Therefore, we could confirm the racemization did not occur at both the ozonolysis and the protodesilylation.…”

“…Each specific rotationo f4 is identicalw ith that of literature. [13] Therefore, we could confirm the racemization did not occur at both the ozonolysis and the protodesilylation. Further derivatization of 5 by Sonogashira coupling was achieved to obtain enyne 6.…”

Photochemical reactivity of bis-carbamate photobase generators

“…Starting from commercially available 3,5-dimethoxybenzyl alcohol (1) the corresponding chloroformate (2) was prepared by treating 1 with a toluene solution of phosgene in dioxane at room temperature for approximately three days [14] The 3,5-dimethoxybenzyl chloroformate (2) subsequently reacted with 1adamantanemethylamine (Ad-amine) in the presence of sodium bicarbonate at room temperature afforded corresponding adamantyl monocarbamate (3) (DMCBzA, PBG) in 98% yield. The monocarbamate (3) obtained was further reacted with 3,5-dimethoxybenzyl chloroformate in presence of lithium bis(trimethylsilylamide) (LHMDS) at -78°C providing the biscarbamate (4) in 85% yield [15] . Further synthesis details will be presented elsewhere.…”

α‐Heterosubstituted β‐Alkylacroleins as Useful Multisubstituted Dienophiles for Enantioselective Diels–Alder Reactions

“…According to the method reported by Burk et al, [14] a variety of b-alkyl and b-aryl derivatives of 6 can be synthesized with complete Z-selectivity by changing the starting aldehyde (R 3 CHO). The acylation of the carbamoyl nitrogen atom [15] of 6 with methyl 2-(chlorocarbonyl)benzoate and subsequent removal of the tert-butyloxycarbonyl (Boc) group gave 7 a. Treatment of 7 a with 1,8-diazabicycloA C H T U N G T R E N N U N G [5.4.0]undec-7-ene (DBU, 13 mol %) gave 8 in an overall yield of 46 %.…”