On the lithium dimethylcuprate induced conversion of propargylic esters into allenes using a steroidal C/D fragment derived from vitamin D3 as a stereochemical probe.

On the Stereochemistry of Organocopper Mediated Conversion of Propargylic Esters to Allenes

“…Besides the similarity in yields and stereoselectivities, small amounts of the reduction product 10 are produced. On the basis of these results [9] , the recent reports by the Schering group [1Db] and Vermeer and co-workers [l Oa] , and the even earlier results from a number of laboratories including our own [2][3][4][5][6]8], there appears to be no reported exception to the notion that the organocopper promoted conversion of propargylic esters into allenes originates from an anti mode of displacement (Scheme 1). Depending upon conditions and substrates, however, the degree of stereoselectivity is highly variable.…”

“…In the specific case of our vitamin D synthetic studies, using the system 3b or 3c in a reaction with vinylcuprates, we found in 1978 that the anti mode of attack was favored [1,2,8] . WesubsequentIy reported [9] that the attack of the more classical Gilman reagent (CH 3hCuLi on 3b-d and 4b-d is strongly anti. This was in agreement with the recent findings by Vermeer [l Oa] and the Scheringgroup [l Ob] ,who confirmed the original stereochemical result (anti) reported by Crabbe [3c] .…”

“…This was in agreement with the recent findings by Vermeer [l Oa] and the Scheringgroup [l Ob] ,who confirmed the original stereochemical result (anti) reported by Crabbe [3c] . In this article, we report the full account of our preliminary communication [9] and describe new investigations of the substrates 3b-d and 4b-d with other Gilman-type reagents as well as the convenient higher-order mixed cuprate system described by Lipshutz [11] . RESULTS …”

From Allylic Sulfoxides to Allylic Sulfenates: Fifty Years of a Never-Ending [2,3]-Sigmatropic Rearrangement

“…Finally, Okamura and co-workers have extensively studied the reactivity of allenyl sulfoxides, obtained through Mislow–Braverman–Evans rearrangement, in a search for approaches to the synthesis of drimanes, retinoids, and vitamin D derivatives. − In a selected example of their investigations (Scheme ), , β-ionone was transformed into Z propargylic alcohol 516 , which underwent sulfenate–sulfoxide rearrangement upon treatment with PhSCl and Et 3 N. Allenyl sulfoxide intermediate 517 was not observed because it evolved through two competitive processes. For compounds with small R groups (R = H, Me, Et), the preferred pathway is a stereospecific six-electron electrocyclization leading to a Z / E mixture of drimatriene derivatives 518 .…”

Rearrangements of sulfoxides and sulfones in the total synthesis of natural compounds

“…47 The addition of the alkyne fragment to the carbonyl group followed by desulfinylation of allenyl sulfoxides under the action of MeLi was used for the preparation of steroids containing allene substituents. 48,49 In the study, 50 allenyl sulfoxides were utilised as the starting compounds in the development of a general method for the preparation of 2,5-dihydrofuranones 57 by cyclisation of substituted allylic alcohols 58, which are products of the [2,3]-rearrangement of allyl sulfoxides 59. The compounds 59 were prepared by the addition of a sodium derivative of dimethyl malonate to allenyl sulfoxides.…”