Über eine [3 + 1]‐Cycloaddition, II. Reaktionen von 4,5‐Dihydro‐1,3,5‐oxazaphosph(V)olen, VI

Abstract

4,S-

The role of substituents in controlling the mode of intramolecular cycloaddition of nitrile ylides

“…This material was prepared by a modification of the procedure developed by Burger and coworkers.38 Thermolysis or photolysis of 4,5-dihydro-1,3,5-X5-oxazaphospholes are known to produce bis(trifluoromethyl)benzonitrile ylides in excellent yield. [39][40][41][42][43] In this case, the only product obtained from the photolysis or thermolysis of 20 was 1,3 cycloadduct 22, mp 140-141 °C. The isolation of 22 strongly suggests that the substituent effect encountered in these nitrile ylide cycloadditions is electronic rather than steric in nature.…”

New strategies for the synthesis of 1- and 2-azetines and their applications as value-added building blocks

“…4E) to 50 , which left the exocyclic imine motif intact. 77 Hydride reduction of 1-azetines offers a viable strategy to access the valuable azetidine scaffold in a straightforward manner.…”

New Strategies for the Synthesis of 1- and 2-Azetines and Their Applications as Value-Added Building Blocks

“…60 Finally, Burger and co-workers disclosed an intriguing example of a LiAlH4 reduction of 49 (Fig 4E ) to 50, which left the exocyclic imine motif intact. 67 Hydride reduction of 1-azetines offers a viable strategy to access the valuable azetidine scaffolds in a straightforward manner.…”

“…Interestingly, the 2-azetine precursors were generated by a three to four step telescoped sequence from a substituted-Boc-protected azetidine, and the nitrile oxides were generated in situ. Monosubstituted 2azetines gave single products (67), but disubstituted 2-azetines gave a mixture of regioisomers (67 and 68) with a maximum regioselectivity of 16:1 (the identity of the major regioisomer is substrate dependent). 78 Another useful class of reactivity to access fused-azetidine scaffolds from 1-and 2-azetines involves cycloaddition with ketenes and isocyanates (Fig.…”