Table 1.

Pyran cyclization equilibrium constants^a for 1 and 2 in various deuterated solvents correlated with solvent dielectric constants (ε)

solvent	Keq (1)	Keq (2)	ε
DMSO-d6	14(2)	8(3)	46.7
DMF-d7	6.9(7)	n/a b	36.7
acetonitrile-d3	6.1(8)	5(1)	37.5
acetone-d6	2.3(4)	2.0(6)	20.7
THF-d8	1.6(2)	1.5(1)	7.58
dichloromethane-d2	1.2(2)	1.8(4)	8.93
chloroform-d	0.41(5)	0.5(2)	4.81

^aK_eq = [1b]/[1a] or K_eq = [2b]/[2a].

^bIntegration data not acquired due to convolution of signals in the ¹H NMR spectrum.