I have three Syringa 'Sensation'. They were planted (by professional gardeners) this past spring.
Dear Gardener: It sounds like the Syringa are suffering from being newly planted in the spring (called transplant shock) and then were followed by a hot, dry summer. I am not surprised that they did not bloom as they may be young. I suspect that they will do better next year after they have settled in. They should produce new growth, but maybe not flowers as they clearly were stressed this year. Be sure that they are well watered before the ground freezes this winter (usually around Christmas) and that they remain well watered next spring and summer. The plants have to settle in and spread their roots, then you will see flowers and lush new growth.