Table 1.

Synthesis of spiropyrans C2–C12SP.

Entry	n	Bromoacid	Alkylation conditionsa	Condensation conditionsb	Product	Yield from 1
1	1	2a	method A	–	C2SP	0%
2	1	2a	method Bc	method Cc	C2SP	21%
3	2	2b	method A	method C	C3SP	81%
4	3	2c	method A	–	C4SP	0%
5	3	2cd	method A	method D	C4SP	38%
6	5	2d	method B	method C	C6SP	52%
7	5	2d	method A	method C	C6SP	71%
8	5	2d	method Ae	method C	C6SP	48%
9	7	2e	method A	method C	C8SP	60%
10	9	2f	method A	method C	C10SP	82%
11	11	2g	method A	method C	C12SP	67%

^aMethod A: Solution of bromoacid (1 equiv) and 2,3,3-trimethylindolenine (1 equiv) in acetonitrile (0.6 M) heated at 80 °C without a condenser for 20 h; Method B: Solution of bromoacid (1 equiv) and 2,3,3-trimethylindolenine (1 equiv) in acetonitrile (0.6 M) heated at reflux for 72 h. ^bMethod C: Solution of crude indolium salt (1 equiv), salicylaldehyde 5 (1 equiv) and piperidine (1 equiv) in MEK (50 mM) heated at reflux for 20 h; Method D: (i) Solution of crude indolium salt (1 equiv) and salicylaldehyde 5 (1 equiv) in ethanol (0.1 M) heated at reflux for 20 h then (ii) solution of crude spiropyran stirred in 2:1 THF/NaOH (50 mM). ^cConducted at room temperature. ^dReaction used ethyl 4-bromobutyrate. ^eConducted without solvent.