A new approach to 19-nor-A-ring phosphine oxide for the convergent synthesis of 19-nor-calcitriol

•An efficient synthesis of 19-nor-A-ring phospine oxide (5) was achieved from (S)-carvone (7%, 15 steps).•A convergent synthesis of 1α,25-dihydroxy-19-norvitamin D3 (3) was achieved from (S)-carvone and Inhoffen-Lythgoe diol (20 steps, 3%).•The triene system assembly is based on a Wittig-Horner coupling. [Display omitted] A new approach to 19-nor-A-ring phosphine oxide 5 together with a convergent synthesis of the vitamin D3 analogue 1α,25-dihydroxy-19-norvitamin D3 (3) have been developed. The 19-nor-A-ring is constructed from (S)-carvone. The triene system is assembled by a Wittig-Horner coupling.