Fert-Butoxycarbonyl group

Keywords A-fert-butoxycarbonyl group, Yb(OTf)3, silica gel, amide... 

Rather more conventional means were used to remove an alkyl silyl ether in the presence of an ary silyl ether in a synthesis of Dynemicin Here the task was simply accomplished with HF in acetonitrile [Scheme 4.56].92 Acidic conditions also prevailed in a synthesis of Doliculide wherein an alkyl tert-butyl ether, a tert-butyl ester and an N-fert-butoxycarbonyl group were cleaved simultaneously without challenge to the remaining aryl silyl ether [Scheme 4.57] ... 

Keywords A -fert-butoxycarbonyl group, aluminium chloride, microwave irradiation, amine... 

To illustrate the specific operations involved, the scheme below shows the first steps and the final detachment reaction of a peptide synthesis starting from the carboxyl terminal. N-Boc-glycine is attached to chloromethylated styrene-divinylbenzene copolymer resin. This polymer swells in organic solvents but is completely insoluble. ) Treatment with HCl in acetic acid removes the fert-butoxycarbonyl (Boc) group as isobutene and carbon dioxide. The resulting amine hydrochloride is neutralized with triethylamine in DMF. 

A versatile activating group for the removal of a-protons that are not benzylic is the carbamate fert-butoxycarbonyl, or t-Boc group, developed for this purpose by Beak and Lee in 1989. Its utility derives from the fact that the Boc group is easy to attach to a secondary amine, and easy to remove after a deprotonation/alkylation sequence. Moreover, stannylation affords a-amino-organostannanes that are themselves useful precursors of a-amino-organolithium compounds (Scheme 29) (see Section II). In a chiral pyrrolidine system, it has been shown that both deprotonation (H Li) and methylation (Li Me) occur with retention of configuration. 

The vinyl triflate of Komfeld s ketone has been subjected to Heck reactions with methyl acrylate, methyl methacrylate, and methyl 3-(7V-fert-butoxycarbonyl-A -methyl)ammo-2-methylenepropionate leading to a formal synthesis of lysergic acid [259]. A similar Heck reaction between l-(phenylsulfonyl)indol-5 yl triflate and dehydroalanine methyl ester was described by this research group [260]. Chloropyrazines undergo Heck couplings with both indole and 1-tosylindole, and these reactions are discussed in the pyrazine Chapter [261]. Rajeswaran and Srinivasan described an interesting arylation of bromomethyl indole 229 with arenes [262]. Subsequent desulfurization and hydrolysis furnishes 2-arylmethylindoles 230. Bis-indole 231 was also prepared in this study. 

The methyl ester 8a, prepared from commercially available 3,4-diaminobenzoic acid, has been reacted with N,N -di(fert-butoxycarbonyl)thiourea in the presence of mercury chloride to provide the C3 guanylated intermediate 8b. The selectivity observed in this reaction arises from the decreased nucleophilicity of the C4 amino group due to the electron withdrawing para carbomethoxy functionality. 

Amino groups are often protected as their fert-butoxycarbonyl amide (BOC) derivatives. The BOC protecting group is introduced by reaction of the amino acid with di-tcrt-butyl dicarbonate in a nucleophilic acyl substitution reaction (Section 21.5) and is removed by brief treatment with a strong organic acid such as trifluoroacetic acid, CFgCOOH. 

A related N-terminal-protecting group is fert-butoxycarbonyl, abbreviated Boc ... 

Hg. 7.9. Structure showing the self-inclusion of a butoxycarbonyl group of 6-deoxy-6- 4-[A/-fert-butoxycarbonyl-N-... 

Hydrogen bromide may be used to remove either the benzyloxycarbonyl or fert-butoxycarbonyl protecting group. The benzyloxycarbonyl protecting group may also be removed by catalytic hydrogenolysis. Fmoc is removed in base. 

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