Preparation of a Storable Zinc Carbenoid Species and Its Application in Cyclopropanation, Chain Extension, and [2,3]-Sigmatropic Rearrangement Reactions

Abstract

The formation of a new phosphate carbenoid (n-BuO)(2)P(O)OZnCH(2)I and its application in organozinc-mediated reactions is described. This carbenoid undergoes very slow degradation in solution and can be stored for several weeks at -20 degrees C. Its reactivity was tested with many representative alkenes and was determined to be a powerful cyclopropanating reagent, giving the corresponding cyclopropanes in 72-99% yield. The use of this carbenoid in the chain extension of 1,3-diketones and [2,3]-sigmatropic rearrangement reactions is also described.

Highly Efficient Asymmetric Simmons–Smith Cyclopropanation Promoted by Chiral Heteroorganic Aziridinyl Ligands

“…(1 S ,2 S )‐2‐(2‐Phenylethyl)cyclopropylmethanol (6; Table 2 , entry 3): Colorless oil; 1 H NMR (600 MHz, CDCl 3 ): δ =0.35–0.40 (m, 2 H), 0.51–0.54 (m, 1 H), 0.82–0.85 (m, 1 H), 1.53 (br s, 1 H), 1.55–1.67 (m, 2 H), 2.72–2.78 (m, 2 H), 3.40–3.43 (m, 2 H), 7.21–7.25 (m, 3 H), 7.28–7.32 ppm (m, 2 H). Other spectroscopic data of compound 6 are in agreement with the literature 7…”

“…In this case, the stereoselective Simmons–Smith reaction catalyzed with chiral ligands serves as an effective method for the preparation of cyclopropylmethanol derivatives, which are useful building blocks for organic synthesis 3–6. Of many approaches to the enantioselective cyclopropanation, the methods using phosphate carbenoid, ( n BuO) 2 P(O)OZnCH 2 I,7 titanium TADDOLate,8 Ru(II)‐Pheox catalyst,9 and dioxaborolane ligands10 are notable.…”

Pentafulvene for the Synthesis of Complex Natural Products: Total Syntheses of (±)‐Pallambins A and B

“…Substantial experimentation was necessary to identify reaction conditions that led to reaction of the endocyclic olefin and the desired exo selectivity. Established cyclopropanation protocols such as ZnEt 2 /CH 2 I 2 ,8a ZnEt 2 /CH 2 I 2 /F 3 CCO 2 H,8b ZnEt 2 /CH 2 I 2 /( n BuO) 2 P(O)OH,8c and i Bu 3 Al/CH 2 I 2 8d suffered from low conversion and poor chemoselectivity. In contrast, when 6 was subjected to Denmark′s conditions (ZnEt 2 /ClCH 2 I), the desired cyclopropane was isolated as a single diastereomer in 85 % yield (Scheme ) 8e.…”

Intermolecular Stetter Reactions on Morita‐Baylis‐Hillman Adducts: an Approach to Highly Functionalized 1,4‐Dicarbonyl Compounds

“…For example, the nucleophilic substitution of α ‐haloketones by enolates is a robust method to access 1,4‐diketone compounds . Other alternative methods that are often employed, include conjugate addition of enolates to Michael acceptors, oxidative coupling of enolates, organo‐cobalt and organo‐samarium additions, homologation reactions of 1,3‐dicarbonyl compounds and the C ‐acylation of styrenes . Stetter reactions between aldehydes and Michael acceptors catalyzed by N‐ heterocyclic carbenes (NHC's) present a powerful approach to access 1,4‐dicarbonyls .…”