𝔖 Bobbio Scriptorium
✦   LIBER   ✦

Synthesis of 6H-1,2-oxazines by hetero Diels-Alder reactions of nitroso alkenes towards methoxyallenes

✍ Scribed by Zimmer, Reinhold ;Reißig, Hans-Ulrich

Publisher
John Wiley and Sons
Year
1991
Tongue
English
Weight
686 KB
Volume
1991
Category
Article
ISSN
0947-3440

No coin nor oath required. For personal study only.

✦ Synopsis

6H-1,2-Oxazines / Methoxyallene / Nitroso alkene / Hetero Diels-Alder reaction Regioselective hetero Diels-Alder reactions of in-situ generated nitroso alkenes 2-4 with methoxyallene derivatives 1 provide 4H-1,2-oxazines 5-7 with an exo-methylene group at C-5. These primary cycloadducts are smoothly transformed into conjugated GH-1,2-oxazines 11 -13 by base or acid catalysis. The bicylic nitroso alkene 17 and methoxyallene (1 a) combine to give the tricyclic 1,2-oxazine 18, thus demonstrat-ing that an exo-transition state is favoured in this [4+2] cycloaddition. The reaction of the sterically hindered methoxyallene 1 h with nitrosostyrene affords the cycloadduct 22 in low yield. 22 is very likely formed by a two-step Diels-Alder reaction via a zwitterion. Allene derivatives lacking a methoxy group are not sufficiently reactive towards nitroso alkenes and do not provide 1,2-oxazines.

📜 SIMILAR VOLUMES

Synthesis of trialkylsiloxy-substituted
Synthesis of trialkylsiloxy-substituted and other 5,6-dihydro-4H-1,2-oxazines by hetero diels-alder reactions of nitroso alkenes — Preparative scope and diastereoselectivity
✍ Hippeli, Claudia ;Reißig, Hans-Ulrich 📂 Article 📅 1990 🏛 John Wiley and Sons 🌐 English ⚖ 857 KB

## Abstract A variety of 5,6‐dihydro‐4__H__‐1,2‐oxazines 3 and 4 is prepared in good yields from silyl enol ethers 1 and nitroso alkenes 2a or 2b, respectively. A systematic variation of substituents reveals preparative scope and limitations of this hetero Diels‐Alder reaction with inverse electron