Stereoselectivity of cyclization of substituted 5-hexen-1-yllithiums: regiospecific and highly stereoselective insertion of an unactivated alkene into a carbon-lithium bond

Stereochemistry of the cyclization of 4-(t-butyldimethyl)siloxy-5-hexenyllithium: cis-selelective ring-closure accompanied by retro-[1,4]-Brook rearrangement

“…Some time ago we reported7 that cis-[2-(t-butyldimethylsiloxy)cyclopentylmethyl]lithium (11), which gives 8 upon quench with MeOH, is prone to a facile, intramolecular [1,4]-C→O migration of the silyl group (a retro-[1,4]-Brook rearrangement). 9 As illustrated below, this rearrangement is confined exclusively to 11; the trans-isomer (12) is completely stable with respect to silyl migration.…”

“…General spectroscopic and chromatographic procedures, methods used for the purification of reagents and solvents, and precautions regarding the manipulation of organolithiums have been previously described. 1,5,12 The concentration of commercial solutions of t-BuLi in pentane was determined immediately prior to use by the method of Watson and Eastham. 13 The preparations of 3-[(t-butyldimethyl)siloxy]-6-iodo-1-hexene (6), trans-2-methyl-1-(t-butyldimethylsiloxy)cyclopentane (7), cis-2-methyl-1-(t-butyldimethylsiloxy)cyclopentane (8), and cis-2-[(t-butyldimethylsilyl)methyl]cyclopentanol (9) have been previously described.…”

“…The results of these studies demonstrate that the ring closure, which is cis-selective in all of the solvent systems investigated, is accompanied by a facile [1,4] …”

“…The well-studied 5-exo cyclization of 5-hexenyllithiums, which involves a chair-like transition state in which the Li-atom is intramolecularly coordinated to the C(5)-C(6) π-bond, 1 has been used to prepare a variety of carbocyclic 2 and heterocyclic 3 ring systems. The cyclization of 5-hexenyllithiums bearing heteroatomic substituents capable of intramolecular coordination to the Li-atom has received less attention.…”

(−)-Sparteine-Mediated Asymmetric Intramolecular Carbolithiation of Alkenes: Synthesis of Enantiopure Cyclopentanes with Three Consecutive Stereogenic Centers

“…Furthermore, the achiral bicyclic product 9 (R H ) was isolated in small quantities in the presence of the sterically demanding diamine 1, whereas 9 was formed in nearly quantitative yield of 93% in the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA) instead of 1 (Scheme 3). The steric bulk at the Li center and the reaction temperature were the major parameters affecting the intramolecular nucleophilic attack of the benzylic lithium species at the C(1), with the carbamate acting as a leaving group 7 ). The relative configuration of 8a was assigned as trans by NOE measurements showing a strong NOE of the benzylic protons and the proton at C(1).…”