Homoallyl alcohols cyclization

Tetrahydrofurans. Homoallylic alcohols cyclize to tetrahydrofurans on reaction with T1(OAc)3.1... 

Cyclopropanation. Certain homoallylic alcohols cyclize in the presence of... 

Additions of silylated ketene acetals to lactones such as valerolactone in the presence of triphenylmethyl perchlorate in combination with either allyltrimethylsilane 82, trimethylsilyl cyanide 18, or triethylsilane 84b, to afford substituted cyclic ethers in high yields have already been discussed in Section 4.8. Aldehydes or ketones such as cyclohexanone condense in a modified Sakurai-cyclization with the silylated homoallylic alcohol 640 in the presence of TMSOTf 20, via 641, to give unsaturated cyclic spiro ethers 642 and HMDSO 7, whereas the 0,0-diethyllactone acetal 643 gives, with 640, the spiroacetal 644 and ethoxytrimethylsilane 13b [176-181]... 

Recently, a new multicomponent condensation strategy for the stereocontrolled synthesis of polysubstituted tetrahydropyran derivatives was re-published by the Marko group, employing an ene reaction combined with an intramolecular Sakurai cyclization (IMSC) (Scheme 1.14) [14]. The initial step is an Et2AlCl-promoted ene reaction between allylsilane 1-50 and an aldehyde to afford the (Z)-homoallylic alcohol 1-51, with good control of the geometry of the double bond. Subsequent Lewis acid-media ted condensation of 1-51 with another equivalent of an aldehyde provided the polysubstituted exo-methylene tetrahydropyran 1-53 stereoselectively and... 

A fourfold anionic sequence which is not initiated by a Michael but an aldol reaction has been reported by the group of Suginome and Ito (Scheme 2.129) [295]. In this approach, the borylallylsilane 2-573 reacts selectively in the presence of TiCl4 with two different aldehydes which are added sequentially to the reaction mixture. First, a Lewis acid-mediated allylation of the aldehyde with 2-573 takes place to form a homoallylic alcohol which reacts with the second aldehyde under formation of the oxenium ion 2-574. The sequence is terminated by a Prins-type cyclization of 2-574 and an intramolecular Friedel-Crafts alkylation of the intermediate 2-575 with formation of the fraws-1,2-be rizoxadeca lines 2-576 as single diastereomers. 

Ti-mediated cyclization of a l,2-dien-6-yne generates a new allylic titanacycle, which reacts with an aldehyde to give a homoallylic alcohol with high diastereoselec-tivity (Scheme 16.72) [78]. 

Bartlett PA, Johnson WS, Elliott JD (1983) Asymmetric synthesis via acetal templates. 3. On the stereochemistry observed in the cyclization of chiral acetals of polyolefinic aldehydes formation of optically active homoallylic alcohols. J Am Chem Soc 105 2088-2089... 

Cross-Cyclization of Epoxides with Homoallylic Alcohols. 232... 

Table 1 Cross-cyclization of epoxides with homoallylic alcohols...

Tetrahydropyrans hydroxylated at the 4-position have good synthetic value [113]. Although many synthetic methods have been reported [17-23,114,115], the search for potential alternate approaches and the development of eco-friendly and high-yielding reactions resulted in the development of a method that poses less problems for the environment. Synthesis of tetrahydropyranol derivatives can be achieved through the Prins-type cyclization reaction of homoallylic alcohols with aldehydes using bismuth triflate as catalyst in [bmim]PF6 solvent system [108] (Fig. 22). 

Sulfonyl-substituted homoallylic alcohols tmdergo 5-endo-trig cyclization reactiorrs on treatment with base, with cyclization stereoselectively depending on double bond geometry, to give substituted tetrahydrofurans <99T13471>. 

Cyclofunctionalization of homoallylic alcohols with bis(sym-collidine)iodine(I) perchlorate produces oxetanes in good yield if the 4-exo mode of cyclization is favored electronically by the alkene substitution pattern (Table l).14 Geminal substitution at the carbinol carbon also favors this mode of cyclization (compare entries 2 and 3 with entry 1). Substitution at C-3 leads to reaction only by the 4-exo mode (entry 4), while substitution at C-4 leads to cyclization only via the 5-endo mode (entry 5). 

Table 1 Cyclization of Homoallylic Alcohols with I(colIidine)2+ CIO4 ...

Table 16 O-Cyclizations of Derivatives of Acyclic Homoallylic Alcohols (Equation 55)...

Studies on tethered derivatives of homoallylic alcohols are fewer in number. Iodocyclization of tri-chloroacetimidate derivatives of 4-penten-2-ol (21) gave cis- and franj-dihydrooxazines in an 80 20 ratio,234a 254b while cyclization of the /V-benzenesulfonylcarbamate derivatives (22) provided an 86 14 ratio of cyclic carbamates 253 Cyclization of the N-acylaminomethyl derivatives (23) with mercury(II) tri-fluoroacetate under conditions of kinetic control gave a 75 25 ratio of cis- and rrans-tetrahydrooxazine derivatives, but cyclization under conditions which allowed for equilibration of the organomercury intermediates produced a 6 94 ratio.238... 

Prins cyclization reaction of scalemic homoallylic alcohols (26) with aldehydes (R CIIO), carried out in the presence of an acid catalyst (HX), affords tetrasub-stituted tetrahydropyrans (27) (99% ee) with high stereoselectively in good yields... 

Anhydrous iron(III) halides catalyse coupling of alkynes and aldehydes.211 Simple terminal alkynes, R CH, react with aldehydes, R2CHO, to give ( ,Z)-1,5-dihalo-1,4-dienes (55). In contrast, non-terminal arylalkynes give ( ,)-o, /3-unsaturated ketones. The catalysts also promote standard Prins cyclization of homoallylic alcohols. Studies of intermediates and of alkyne hydration - together with calculations - all support FeX3 complex formation with alkyne as the activating step. 

Epoxides undergo cross-cyclization with homoallylic alcohols in the presence of zirconium tetrachloride under mild conditions to give the corresponding tetrahydropyran derivatives (Scheme 45).75... 

Phenylselenoetheriflcation (10, 18).1 Cyclization of the homoallylic alcohol 1 with C6H5SeCl and K2C03 to a 2,5-disubstituted tetrahydrofuran (2) proceeds with... 

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