Highly Efficient Synthesis of cis-[3]Cumulenic Diols via Zirconocene-Mediated Coupling of 1,3-Butadiynes with Aldehydes

Abstract

A highly efficient and convenient method for the monozirconation of silyl- or tert-butyl-substituted 1,3-butadiynes using the Negishi reagent has been developed. The resulting zirconium butadiyne complexes undergo two syn-SE2′ reactions with various aldehydes to yield the cis-[3]­cumulenic diols with moderate to high diastereoselectivities. The silyl substituents at the butadiyne terminus show remarkable influence on the diastereoselectivity.

Unexpected Zirconium‐Mediated Multicomponent Reactions of Conjugated 1,3‐Butadiynes and Monoynes with Acyl Cyanide Derivatives

“…Herein, we also report the diverse reactivity of these zirconacycles toward aroyl cyanides and alkyl cyanoformates, the resulting reactions involving an insertion of a cyanide group into the metal-butadiyne complexes as the initial step (Scheme 1). [9] In addition, we show that this reactivity is also exhibited by zirconocene-monoyne complexes.As demonstrated in our recent study, [6] treatment of 1,3butadiyne 1, which bears bulky silyl groups, with the Negishi reagent resulted in the formation of zirconacyclocumulene 3 as a major product, which is possibly in equilibrium with the three-membered alkynylzirconacyclopropene 2, although the equilibrium lies predominantly on the side of 3. Interestingly, 2/3 undergoes a novel reaction when treated with carbamoyl cyanides (Table 1).…”

“…As demonstrated in our recent study,6 treatment of 1,3‐butadiyne 1 , which bears bulky silyl groups, with the Negishi reagent resulted in the formation of zirconacyclocumulene 3 as a major product, which is possibly in equilibrium with the three‐membered alkynylzirconacyclopropene 2 , although the equilibrium lies predominantly on the side of 3 . Interestingly, 2 / 3 undergoes a novel reaction when treated with carbamoyl cyanides (Table 1).…”

“…8 We suggested that five‐membered zirconacyclocumulenes were formed in these reactions, based on an NMR study of the zirconium intermediates and single‐crystal X‐ray analysis of [Cp 2 Zr(η 4 ‐1,2,3,4‐ t BuC 4 t Bu)]. These complexes undergo two sequential syn ‐S E 2′ reactions with various aldehydes to yield the cis ‐[3]cumulenic diols, which represents the first example of a product derived from the addition of two molecules of aldehyde to a metal‐coordinated butadiyne complex 6. In this communication, we report an unprecedented zirconium‐mediated multicomponent reaction of 1, 3‐butadiynes with carbamoyl cyanides to give azazirconacycles containing a 1,4‐benzodiazepin‐2‐one skeleton; the cascade reaction involving an interesting CH functionalization of N ‐aryl rings on carbamoyl cyanides.…”

“…For this novel transformation, we tentatively propose the mechanism outlined in Scheme . First of all, an equilibrium between zirconacyclopentatriene 3 and zirconacyclopropene 2 exists in the reaction mixture; 3 is likely to be the dominant species, whereas 2 is more reactive 6. 7a An S E 2′‐type addition of the CN group of carbamoyl cyanides to the less hindered propargyl zirconium moiety in complex 2 takes place to deliver an azazirconacyclocumulene 8 , which might isomerize to azazirconacyclopentadiene 10 ; however, we still cannot exclude the reaction pathway for 10 involving direct insertion of a cyano group into the ZrC bond close to the R 1 group of 2 17.…”

“…These complexes undergo two sequential syn-S E 2' reactions with various aldehydes to yield the cis- [3]cumulenic diols, which represents the first example of a prod-uct derived from the addition of two molecules of aldehyde to a metal-coordinated butadiyne complex. [6] In this communication, we report an unprecedented zirconium-mediated multicomponent reaction of 1, 3-butadiynes with carbamoyl cyanides to give azazirconacycles containing a 1,4-benzodiazepin-2-one skeleton; the cascade reaction involving an interesting C À H functionalization of N-aryl rings on carbamoyl cyanides. Herein, we also report the diverse reactivity of these zirconacycles toward aroyl cyanides and alkyl cyanoformates, the resulting reactions involving an insertion of a cyanide group into the metal-butadiyne complexes as the initial step (Scheme 1).…”