Table 2.

Cycloaddition of the nitrones 20a-20e and alkenylphosphonates 23–25.

Nitrone	Nucleobase B	Alkene	Reaction time (h)a	Cis/trans ratio	Yield [%]
20a		23 24 25	30 30 30	80:20 72:28 89:11	27a – 22b; 27a + 28a – 24c 29a – 16b; 29a + 30a – 32c; 30a – 9b 31a – 30b; 31a + 32a – 13c
20b		23 24 25	10 16 14	74:26 79:21 86:14	27b – 3b; 27b + 28b–10c 29b–13b; 29b + 30b–23c 31b–20b; 31b + 32b–26c
20c		23 24 25	8 21 8	86:14 72:28 70:30	27c – 4b; 27c + 28c – 15c 29c – 12b; 29c + 30c – 3.3c 31c – 19b; 31c + 32c – 10c
20d		23 24 25	8 10 8	71:29 80:20 84:16	27d–21b; 27d + 28d–15c 29d – 5b; 29d + 30d–20c 31d–27b; 31d + 32d – 7c; 32d – 2b
20e		23 24 25	40 26 21	– 80:20 69:31	decompositiond –e –e

^aCycloaddition under MW irradiation.

^bYield of the pure diastereoisomer.

^cYield of the pure mixture of diastereoisomers.

^dDecomposition of the starting nitrone 20e was observed. The unreacted allylphosphonate 23 was recovered almost quantitatively.

^eRatio of diastereoisomeric cycloadducts 29e and 30e as well as 31e and 32e were calculated, however pure isomers could not be isolated from the mixture containing several unidentified products.