Year: 2006
Type: article
Abstract: N-Boc-protected L-proline (6) was converted into the bicyclic lactim ether (8aS)-6,7,8,8a-tetrahydro-1-methoxypyrrolo[1,2-a]pyrazin-4(3H)-one (5) in four steps (Scheme 1). Deprotonation with LDA or LHMDS and subsequent alkylation resulted in the diastereoisomeric products cis- and trans-9. The diastereoselectivity was mainly dependent on the electrophile. Whereas small alkyl halides gave preferably cis-9, sterically more-demanding alkyl halides resulted in cis/trans mixtures. Electrophiles bearing a π-system favored the trans-products 9. Some isolated cis- and trans-lactim ethers 9 were converted to the corresponding diketopiperazines cis- and trans-10 by acid hydrolysis. The structures and configurations of several compounds were confirmed by NMR and NOE experiments, as well as by X-ray crystallography (Figs. 1–4).
Source: Helvetica Chimica Acta
Institution: University of Stuttgart
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2007420572