Heteroatom-substituted allylic reagents

The X-ray crystal structure of A -Boc-A -/7-methoxyphenyl-3-phenylallyI-lithium-(-)-sparteine complex has been reported [184], This structure differs from the previous structure in that the lithium is associated in an -fashion. The lithium-(-)-sparteine complex resides on the Re face of the ally unit. Stannylation of the lithium complex was established to occur with inversion of configuration. 

---

We have developed asymmetric syntheses of isocarbacyclin [3] (Scheme 1.3.2) and cicaprost [4] (Scheme 1.3.3) featuring a Cu-mediated allylic alkylation of an allyl sulfoximine [5-7] and a Ni-catalyzed cross-coupling reaction of a vinyl sulf-oximine [8-10], respectively, transformations that were both developed in our laboratories. The facile synthesis of an allyl sulfoximine by the addition-elimination-isomerization route aroused interest in the synthesis of sulfonimidoyl-sub-stituted aiiyititanium complexes of types 1 and 2 (Fig. 1.3.2) and their application as chiral heteroatom-substituted allyl transfer reagents [11]. 

The addition of heteroatom-substituted allylic anions to aldehydes has found particular interest as it represents a homoaldoi reaction. Metalated allyl carbamates seem to be the most valuable reagents developed for this purpose as they are prepared easily and exhibit high y-selectivity and dia-stereoselectivity, at best in their titanated form (Scheme 79). ... 

Ti reagents bearing heteroatom-substituted allyl residues are conveniently used in analogy with their nonsubstituted analogs to prepare homoallylic alcohols with sulfur, silicon, - phosphorus, and other -substituents. These groups can be subsequently exploited to introduce further functions. As the topic will be extensively covered in Part 1 of Volume 2, only a few salient aspects of chemo-, regio-and diastereo-selectivity of such reagents will be considered in this section. 

Several examples for allylic reagents further substituted by heteroatoms are known. For example, a mixture of the l,l-dichloro-2-alkene and the l,3-dichloro-1-alkene leads to a homogeneous homoallylic alcohol17,18. 

As well as alkenylstannanes [106-108], other classes such as a-heteroatom-substituted alkyltributylstannanes [109] and, more importantly, allylic stannanes [110, 111] also undergo these Sn-Cu transmetalations. Otherwise difficult to prepare, allylic copper reagents may, however, be obtained by treatment of allylic stannanes (produced in turn from organolithium, magnesium, or zinc organometallics) with Me2CuLi LiCN. They enter into cross-coupling reactions with alkyl bromides [110] or vinyl triflates (Scheme 2.52) [111]. 

Vinylcyclopropanols have been prepared by the addition of alkenyl Grignard reagents to a variety of cyclopropanone equivalents. Upon treatment with acid, the vinylcyclopropanols rearrange to o-substituted cyclobutanones. Alternatively, a variety of o-heteroatom-substituted cyclopropyl lithium reagents have been developed. These react with aldehydes and ketones to afford cyclopropylcarbinols which also rearrange to cyclobutanones under acid catalysis.Lastly, vinylcyclopropanols and cyclopropylcarbinols have been prepared by the cyclopropanation of enol silyl ethers and allylic alcohols. 

Chiral Dialkylboranes. Several allylic boranes have been developed as chiral auxiliary reagents (Fig. 5). The introduction of terpene-based reagents such as 12 and 64-68 has been pioneered by H.C. Brown, and the most popular class remains the bis(isopinocampheyl) derivatives (structures 12, 64-66). A wide variety of substituted analogs have been reported, including the popular crotylboranes but also a number of other reagents bearing heteroatom-... 

Regarding bond formation between carbon and one heteroatom, 1,4,2-dioxazine 168 was obtained via intramolecular nucleophilic substitution on 3-hydroxyisoindolone 167 (Equation 43) <1999TL2117>. A milder cyclization procedure was employed in the preparation of 1,4,2-dioxazine 170 from substrate 169, by means of the Burgess reagent ((methoxycarbonylsulfamoyl)triethylammonium A -betaine) (Equation 44) <2001JMC619>. 0-Allyl hydroxamic acids 171 cyclize with phenylselenenyl sulfate to give 1,4,2-dioxazines 172 (Equation 45) <1995CC237>. 

---