Boc-BMI -

Preparative Methods the commercial glycine Wmethylamide hydrochloride is converted to the racemic imidazolidinone (2) by imine formation with Pivalaldehyde and cyclization under acidic conditions (eq 1). The mandelate salt of like configuration is less soluble and is used for highly efficient resolution subsequent treatment with Boc anhydride (Di-t-butyl Dicarbonate) gives the enantiomeric Boc-BMI (1) (eq 2). 

Reactions of Boc BMI with Electrophiles. The enolate of Boc-BMI is generated with Lithium Diisopropylamide in THF at -75 °C the resulting solutions of this highly nucleophilic reagent are stable up to 0 °C. All reactions occur from the face of the enolate trans to the t-Bu group at C(2). Alkylations even with secondary alkyl halides are so efficient, to give (3), that one-pot double alkylations, which yield (4), are possible the sequence in which two different alkyl halides are employed determines the absolute configuration of the ot-branched ot-amino acids eventually obtained. 

The method has been used to prepare isotopically labelled amino acids. While Boc-BMI enolate adds to aldehydes with only moderate diastereoselectivity, reduction of the acylation products (5) gives allothreonine derivatives (6). Michael additions to o(,p-unsaturated esters, ketones, and nitro compounds lead to products of type (7) and (8) (for a general discussion see Suzuki and Seebach ). 

BMI. Radical bromination to give (9) (eq 3), Arbuzov reaction, and alkenation lead to ( )-5-alkylidene-Boc-BMI, to which cuprates add highly diastereoselectively with formation of the imidazolidinones (10) containing two new stereogenic centers (eq4). ... 

Hydrolysis to Nonproteinogenic Amino Acids. Numerous amino acids, including a-branched ones, have been prepared from Boc-BMI. Only a few examples can be alluded to here (11) from (5)-(l), EtI, and Br(CH2)4Cl (12) from (5)-(l), 3-methylbutanoyl chloride, and Lithium Triethylborohydride (13) from (R)-(l), butanal, and dibutylcuprate (14) from (S)-(l) and 4-phenylbut-2-enoate. ... 

Other Synthetic Building Blocks from Boc-BMI. Deoxygenation of Boc-BMI leads to the imidazolidine (16) which can be lithiated on the methylene group next to N(l), and thus converted to compounds (17) from the corresponding ester (R = C02Me), 2,3-diaminopropionic acid derivatives (18) and (19) are available. ... 

---