Table 1. Synthesis of N-Boc-Protected Azobenzene–Alanine Analogues.

entry	X	R	product	yielda (%)
1	H	4-Me (2a)	3a	73
2	H	2-OMe (2b)	3b	72
3	H	4-CN (2c)	3c	72
4	H	3-CN (2d)	3d	85
5	H	3-CH=CH2 (2e)	3e	68
6	H	3-C≡CH (2f)	3f	83b
7	H	2,6-F2 (2g)	3g	95
8	H	2,4,6-F3(2h)	3h	91
9	H	2,6-F2-4-CONH2 (2i)	3i	94c
10	H	2,6-F2-4-I (2j)	3j	82d,e
11	H	2,3,4,5,6-F5 (2k)	3k	89
12	F	2,6-F2 (2g)	3l	72
13	F	2,4,6-F3 (2h)	3m	72
14	F	2,3,4,5,6-F5 (2k)	3n	60
15	Cl	2,6-F2 (2g)	3o	68e,f
16	Cl	2,4,6-F3 (2h)	3p	67f,g
17	Cl	2,3,4,5,6-F5 (2k)	3q	63

^aIsolated yields were reported. Unless noted otherwise, reactions were carried out by stirring a solution of spirolactone (1a–c) with 1.1 equiv of the substituted phenylhydrazine in MeCN at room temperature for 12–17 h.

^b24 h reaction time.

^cMeOH/MeCN (1:4) was used as solvent.

^d1.5 equiv of the substituted phenylhydrazine was used.

^e72 h reaction time.

^f2.5 equiv of the substituted phenylhydrazine was used.

^g48 h reaction time.