Pd-Catalyzed Sulfinylzincation of Activated Alkynes with 1-Alkynyl Sulfoxides as a Sulfinyl Source

Unprecedented Pd-catalyzed sulfinylzincation with 1-alkynyl sulfoxide as a sulfinyl source was developed. Bis-sulfinyl alkenes were formed in good yields on treatment of 1-alkynyl sulfoxides with Et2Zn in the presence of a Pd-catalyst, wherein zinc sulfenate (or sulfinylzinc) species would be generated in situ to undergo highly syn-selective conjugate addition to the 1-alkynyl sulfoxides. By using 3,3-dimethyl-1-butynyl sulfoxides, formation of the bis-sulfinyl alkenes was completely suppressed and the sulfinylzincation of activated alkynes was accomplished. The reaction tolerates various functionalities, and was promoted considerably by the neighboring group participation of the heteroatom at the δ-position in the alkynoates. Stereodivergent synthesis of two diastereomeric vinylic sulfoxides and reaction of the resulting vinylzinc species with electrophiles were also described.