A facile route to 2-substituted N-Boc pyrrolidines

1,2,3-Triazoles

Rapid progress in the synthetic application of benzotriazole derivatives in the last 20 years has resulted in over 1000 scientific papers on the subject. This fact is reflected in Section 5.01.7, which involves almost a half of the volume of this chapter. The section is arranged according to hybridization of the C-α atom and atomic numbers of the atoms in positions β and γ to allow an easy access to the material of interest. Recent discovery of copper catalysis in [3+2] cycloadditions of azides to acetylenes, the so-called ‘click chemistry’, which boosted application of the 1,2,3-triazole derivatives, especially in medicinal chemistry, is presented in Section 5.01.9. From the point of view of practical applications, Section 5.01.11 is organized according to the number, position, and combination of the substituents at the aromatic rings. Another novel feature that has no precedence in the previous editions of Comprehensive Heterocyclic Chemistry is an addition of triazole and benzotriazole complexes with various transitions metals to Section 5.01.4.

Conversion of Five-, Six-, and Seven-Membered Lactams to Racemic or Scalemic 2-Substituted Heterocycles by Amidoalkylation

An efficient method for the synthesis of 2-alkyl- and 2-aryl pyrrolidines, piperidines, and azepanes from lactams, in either racemic or enantiopure form, is presented. The lactam nitrogens are acylated with either Boc anhydride or trans-cumylcyclohexyl (TCC) chloroformate. Selective reduction of the lactam carbonyl to the carbinolamide is followed by treatment with benzotriazole. Substitution of the benzotriazole is accomplished by treatment with organometallics, yielding the 2-substituted heterocycles. With TCC, up to 90% diastereoselectivity is achieved. After diastereomer purification, reductive removal of the auxiliary affords enantiopure 2-substituted heterocycles. A mechanistic hypothesis is presented that details the conformational equilibria of the key step.

Alpha-(N-carbamoyl)alkylcuprate chemistry in the synthesis of nitrogen heterocycles

The conjugate adducts obtained via coupling of alpha-(N-carbamoyl)alkylcuprates with alpha,beta-ynoates, alpha-allenyl esters, or alpha.beta-enoates or enimides undergo N-Boc deprotection and cyclization onto the ester functionality upon treatment with PhOH/TMSCl, catecholboron bromide, or trimethylsilyl triflate. This two-pot sequence provides synthetic routes to 4-alkylidinepyrrolidine-2-ones, 4-alkylidinepyrrolizidin-2-ones, and 4-alkylidineindolizidin-2-ones via allenyl esters; pyrrolin-2-ones, tetrahydropyrrolizin-2-ones, and tetrahydroindolizin-2-ones via alpha/beta-ynoates; pyrrolidin-2-ones, pyrrolizidin-2-ones, and indolizidin-2-ones via alpha,beta-enoates or alpha.beta-enimides. The reluctance of gamma-carbamoyl-alpha,beta-enoates to undergo E/Z isomerization requires the use of (Z)-beta-iodo-alpha,beta-enoates readily prepared by the addition of HI to the alkynyl esters for the efficient preparation of pyrrolinones, tetrahydropyrrolizinones, and tetrahydroindolizinones. Utilization of omega-functionalized alpha,eta-ynoates or beta-iodo-alpha,beta-enoates allows for cyclization onto the omega-functionality providing for a synthetic route to quinolizidines.