Thioaldehydes are explored as enophiles in Alder-ene reactions for modification and crosslinking of cis-1,4-polyisoprene. The highly reactive thioaldehydes were generated from thiosulfinates in conventional rubber processing equipment. Monofunctional thiosulfinates were used to graft ester and amide functional groups to cis-1,4-polyisoprene. Oligomeric thiosulfinates were used to crosslink cis-1,4-polyisoprene under mild conditions. The networks formed using these new crosslinking agents are characterized. Good mechanical properties were obtained under optimized crosslinking conditions.