Azirinium ylides from alpha-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

作者：Rostovskii Nikolai V; Novikov Mikhail S^*; Khlebnikov Alexander F; Starova Galina L; Avdontseva Margarita S

来源：Beilstein Journal of Organic Chemistry, 2015, 11: 302-312.

DOI：10.3762/bjoc.11.35

• 2-azabuta-1,3-dienes
• azirines
• diazo compounds
• nitrogen ylides
• 2H-1,4-oxazines

Strained azirinium ylides derived from 2H-azirines and alpha-diazoketones under Rh(II)-catalysis can undergo either irreversible ring opening across the N-C2 bond to 2-azabuta-1,3-dienes that further cyclize to 2H-1,4-oxazines or reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b] oxazoles. Dihydroazireno[2,1-b] oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methyl) ketene generated from 3-diazoacetylacetone under Rh(II) catalysis to give 4,6-dioxa-1-azabicyclo[3.2.1] oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1] deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+ G(d, p)), the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b] oxazole intermediate on acetyl(methyl) ketene followed by aziridine ring opening into atropoisomeric oxazolium betaines and cyclization. Azirinium ylides generated from 2,3-di- and 2,2,3-triaryl-substituted azirines give rise to only 2-azabuta-1,3-dienes and/or 2H-1,4- oxazines.

• 出版日期2015-3-2