Transition metal-catalyzed radical cyclizations: a low-temperature process for the cyclization of N-protected N-allyltrichloroacetamides to trichlorinated .gamma.-lactams and application to the stereoselective preparation of .beta.,.gamma.-disubstituted .gamma.-lactams
摘要:
Cyclizations of N-substituted N-allyltrichloroacetamides, where the substituent is an alkyl, Cbz, Boc, Ts, or Ms group, are catalyzed by a 1:1 mixture of CuCl and bipyridine to give the corresponding beta,gamma-trichlorinated gamma-lactams in high yields. The reactions proceed at temperatures from -78-degrees-C to room temperature. Cyclizations of N-allyltrichloroacetamides of acyclic secondary allylic amines are achieved with good selectivity; the cis/trans ratios of the gamma-lactams formed were dependent on the substituents on the nitrogen atom. The stereochemical outcome is compared with that of free-radical cyclization.
Provided are compounds of Formula I:
and pharmaceutically acceptable salts and esters thereof. The compounds, compositions, and methods provided are useful for the treatment of Flaviviridae virus infections, particularly hepatitis C infections.
Various allyl ethers were converted into the corresponding N-allylcarbamates usingchlorosulfonylisocyanate (CSI) via the stable allylic carbocation rather than β-lactam through [2+2] cycloaddition. The reaction of cinnamyl methyl ether with CSI afforded only methyl N-cinnamylcarbamate at 0°C, but at 20°C, it produced a mixture of methyl N-cinnamylcarbamate and methyl N-(1-phenylprop-2-enyl)carbamate
benzyl carbocations was investigated using the novel technique for comparing the stability of carbocations in solution developed by using a simple CSI reaction with various ethers. The p-methoxycinnamyl carbocation was the most stable in our reactionsystem and the next stable carbocation was the p-methoxybenzyl carbocation. The stability of the other carbocations decreased with methacryl, t-butyl, cinnamyl