Facile synthesis of selenium/sulfur-substituted 3-oxa-bicyclo[4.2.0]octa-1(8),5-diene and tetrahydro-1H-isochromene via sequential three-component conjugate addition/condensation/elimination/[2 + 2] or [4 + 2] cyclization reactions

An interesting sequential three-component reaction provides a facile synthesis of selenium/sulfur-substituted 3-oxabicyclo4.2.0]octa-1(8),5-diene and tetrahydro-1H-isochromene from lithium alkylselenolates or alkylthiolates, 1-alkynylphosphine oxides, and aldehydes. The sequential reaction proceeds via a conjugate addition/condensation/elimination process to form the allene intermediate, which subsequently underwent 2 + 2] or 4 + 2] cyclization reaction to afford bicyclic frameworks.